The Prime Minister has promised to hold talks to renegotiate the terms of the UK’s membership and then put a new deal to the British people in a referendum after the next election.

While Mr Cameron has said he wants Britain to remain inside the EU, Mr Johnson said quitting would not be “fatal” for Britain.

Speaking to reporters at the Global Investment Conference, Mr Johnson said he remained “narrowly in favour” of staying inside the grouping of 27 member states and supported David Cameron’s policy of negotiating a new relationship for Britain in the EU.

But he added: “If that fails then yes, obviously, we should be ready to walk away,” he said. “We should be ready to leave.”

The public would welcome a British exit because people would feel they had won back control over their own lives from Brussels, the Mayor claimed.

“If we are honest, I think, democratically, it would be a shot in the arm because people would suddenly feel, yes, we are running our own destiny again, our politics is entirely independent, British electors can choose the people who are taking decisions that affect their lives.

“That would be a very important benefit.”

However, it would be essential to ensure British businesses did not suffer from losing trade in Europe.

Earlier, Mr Cameron had told the 300 conference delegates that he could negotiate a new relationship for Britain with Europe.

Mr Cameron attacked the “pessimists” who believed he would fail, in a direct rebuke to Tory grandees, such as Michael Portillo and Lord Lawson, who have called for the UK to withdraw from the EU.

“There are some pro European pessimists who say, you have to, in Europe, simply sign up to every single thing that anyone in the EU suggests.

You sign every treaty, you sign everything – there is no alternative.

“I think they are completely wrong,” Mr Cameron said.

“The second group of pessimists say there is no prospect of reforming the EU, you simply have to leave. I think they are wrong too.

“I think it is possible to change and reform this organisation and change and reform Britain’s relationship with it.”

It will be wonderful, a Crossrail for the bike. But until that glad day comes, cyclists have to work out another way west – and it is not obvious.

I did the Harrow Road underpass and roundabout, and was navigating slowly in the estates between Trellick Tower and White City when the heavens opened. I was drenched, freezing, and there was no sign of anything like a cycle path to the west, and I am afraid I almost gave up. I was on the verge of ringing for someone to pick me up when I thought: is this the spirit that built the empire? Man or mouse!

Eventually I hooked up with the Great West Road, and look, there was something claiming to be a cycle path. Huh. I was the only person to use it, and frankly I could see why. It was a joke – endlessly petering out, so that I had to join the hurtling wall of steel on the carriageway.

At one stage I found myself bouncing down an ever-narrowing kerbstone with traffic whizzing towards me at 70mph, until the thing degenerated completely. On one side was a ditch full of nettles, on the other the motorway, and everywhere the crushed indicator lights that told me this was a bad place to be.

Eventually I found a “public footpath” and cycled hopefully along until it became a stream, and I had to carry the bike about 500 yards through mud until I came to a farmyard. The dogs started to bark.

In the distance I could see the M40 on my left, the A40 was somewhere on my right. I had been on the move for almost three hours and I was nowhere near Oxfordshire. I had to make a decision. I opted for the A40 – and it was a joy. The traffic was light and unthreatening, and I had time to enjoy the sights.

The beauty of cycling is that you are a part of the world around you – and yet you move through it untouched. I saw vignettes of comedy and tragedy: a kid ringing a doorbell and running away, a poor tourist dropping her iPhone down a drain. I saw the squashed foxes up close. I saw hostelries offering beer and fine wines and “exotic dancing”. I started to fantasise about the pub lunch I would have – roast beef, all the trimmings, a yard of foaming ale, exotic dancing – and then I realised it would be fatal to stop.

Now I was in Beaconsfield, now Wycombe, and I was going like a train. This is peasy! I was saying, when I saw an obstruction ahead. Billions of years ago there were trillions of little sea creatures who all died and left their chalky skeletons in vast mounds around London. They are called the Chilterns, and they almost killed me. My bike zig-zagged across the road as I tried to fight the gradient; my heart was thudding in my ears; I thought I might peg out – but I was determined to make it to Bledlow Ridge; and when I did, it was sheer heaven.

There is nowhere more beautiful than England in May. The tulips were still out; the hawthorn blossom like gunsmoke across the battlefield; the sun soft; everything surging and budding with spring; and though the old bike was clanking badly now I knew we had almost made it – and wheeee! I went down the other side of the hills like something from Enid Blyton, so fast and for so long that I wore out both brake pads; and after another 10 easy miles I was there.

I had cycled about half the distance I will have to do in August – and it had taken me more than six hours! An old French onion-seller would have beaten me, or a motorised wheelchair.

Oh well, the wind was against me, and next time I will be fitter. And one day soon we will build those giant radial routes out of London so that everyone can enjoy the magic of such a day. The age of the bike is coming.

We Tories look at him – with his pint and cigar and sense of humour – and we instinctively recognise someone who is fundamentally indistinguishable from us. He’s a blooming Conservative, for heaven’s sake; and yet he’s in our constituencies, wooing our audiences, nicking our votes, and threatening to put our councillors out of office. We feel the panic of a man confronted by his Doppelgänger. Omigaaaad, we say to ourselves: they’re stealing our schtick! And we are tempted to do a Nicolas Cage – to overreact, to freak out, to denounce them all as frauds or worse. I think there may have been a few ill-advised insults flying around in the past couple of days.

Well, I would humbly submit that there are better ways of tackling the Ukip problem, if indeed it is really a problem at all. The rise of Farage and Ukip tells us some interesting and important things about what the electorate wants – and it is by no means bad news for the Conservatives. It tells us that the voters are fed up with over-regulation of all kinds, and especially from Brussels. Well, who is going to offer a referendum on the EU? Only the Conservatives – and the trouble with voting Ukip is that it is likely to produce the exact opposite: another Labour government and another five years of spineless and unexamined servitude to the EU.

Or take the Human Rights Act, and yesterday’s astonishing story about a fellow who has been here illegally since 2000, and has just tried to persuade a court that he may not be returned to Iraq – in spite of repeated convictions for drug dealing – because he has tattoos. These tattoos apparently include one of a naked lady, of a kind that may allegedly cause offence in a Muslim country.

As it happens, there is no evidence whatever of anyone being persecuted in Iraq because of his tattoos – even in the Islamist chaos that has followed the removal of Saddam. Why shouldn’t he wear a T-shirt? Why can’t he get the tattoo changed to look like a porpoise or something inoffensive? Why are British courts sitting through this kind of drivel? Why are British taxpayers paying hundreds of millions for the whole carry-on? You read that kind of story, and you can see exactly why people are tempted to go for Ukip – just to give the whole cosy and complacent political establishment a kick in the pants.

It is tempting, but there is only one party that has the remotest chance of getting a grip on this sort of politically correct nonsense, and that is the Conservatives. If you want the party that finally got a grip on mass illegal immigration – after Labour deliberately let the brakes off – it is the Tories. If you want to cut the burdens on small business, it is only the Tories who have a hope of governing and actually doing something about the problem.

Rather than bashing Ukip, I reckon Tories should be comforted by their rise – because the real story is surely that these voters are not turning to the one party that is meant to be providing the official opposition. The rise of Ukip confirms a) that a Tory approach is broadly popular and b) that in the middle of a parliament, after long years of recession, and with growth more or less flat, the Labour Party is going precisely nowhere.

Ed Miliband and Ed Balls were the people who advised Gordon Brown most intimately throughout his profligate reign. It was they who said they had taken Britain “beyond boom and bust” and then produced a spectacular bust.

They have absolutely nothing to say or to offer except to take the Labour Party far to the Left of where it was even under Gordon Brown. Their lead has been cut to single figures in the past few weeks, and if – as I strongly suspect – the economy starts to recover well next year (and perhaps as early as this summer), then that lead will be obliterated.

Now is not the time to do a Nicolas Cage and freak out at our Doppelgängers, or to slag them off just for appearing to think, in large part, what many Conservatives think. Now is the time to keep calm and carry on being Conservative.

Asked whether the London Mayor could one day become prime minister, Mr Cameron replied: “I’d never want to put a limit on what Boris can achieve.”

Mr Johnson has been linked with several possible Tory constituency, including Louth and Horncastle in Lincolnshire where the incumbent MP, the veteran Sir Peter Tapsell, has informed Mr Cameron he is “keeping the seat warm” for the mayor and could stand down at the next general election in 2015.

It would be a trickier task for Mr Johnson to return to the Commons before the election, as his mayoral term runs until 2016 and he would have to do both jobs simultaneously.

Mr Johnson gave his strongest hint yet in a recent BBC TV progamme that he would like a tilt at the top job, telling his interviewer, Michael Cockerell: “If the ball came loose from the back of a scrum, it would be a great thing to have a crack at.”

Speculation earlier this year that Mr Cameron could face a leadership challenge before the next election has faded recently, with the Conservatives reuniting after the death of Lady Thatcher, and the Prime Minister extending the hand of friendship to some of his disaffected backbenchers.

However, senior figures in Downing Street are aware that concerns about Mr Cameron’s future could re-emerge if the Tories suffer a very bad set of results in local elections in May.

Last week, the Prime Minister appointed Mr Johnson’s younger brother Jo Johnson, the Tory MP for Orpington, head of his policy unit at No10 in a surprise move.

Mr Cameron‘s warm words came despite years of rivalry between the two Old Etonians, with many Conservative MPs believing Mr Johnson is manoeuvring to try to succeed Mr Cameron as Tory leader.

That would depend on Mr Johnson becoming an MP once again – possibly before the next general election – a prospect Mr Cameron appeared to entertain in his remarks.

The Prime Minister said: “Boris can do anything, that’s the moral of the story of Boris.

“Boris is one of the greatest assets the Conservative Party has. I love Boris.”

Asked whether the London Mayor could one day become prime minister, Mr Cameron replied: “I’d never want to put a limit on what Boris can achieve.”

Mr Johnson has been linked with several possible Tory constituency, including Louth and Horncastle in Lincolnshire where the incumbent MP, the veteran Sir Peter Tapsell, has informed Mr Cameron he is “keeping the seat warm” for the mayor and could stand down at the next general election in 2015.

It would be a trickier task for Mr Johnson to return to the Commons before the election, as his mayoral term runs until 2016 and he would have to do both jobs simultaneously.

Mr Johnson gave his strongest hint yet in a recent BBC TV progamme that he would like a tilt at the top job, telling his interviewer, Michael Cockerell: “If the ball came loose from the back of a scrum, it would be a great thing to have a crack at.”

Speculation earlier this year that Mr Cameron could face a leadership challenge before the next election has faded recently, with the Conservatives reuniting after the death of Lady Thatcher, and the Prime Minister extending the hand of friendship to some of his disaffected backbenchers.

However, senior figures in Downing Street are aware that concerns about Mr Cameron’s future could re-emerge if the Tories suffer a very bad set of results in local elections in May.

Last week, the Prime Minister appointed Mr Johnson’s younger brother Jo Johnson, the Tory MP for Orpington, head of his policy unit at No10 in a surprise move.

Not only have the Qataris introduced modern medicine to the ancient custom of the camel beauty parade. They follow their camel races in huge Lexus SUVs, so new that the plastic is still on the seats; and they no longer have old-fashioned child jockeys on the back of the camels – they were banned five years ago after some human rights outcry. So now they have electronic jockeys – little whip-wielding robots on the humps, clad in racing silks – and they control them from the backs of their charging SUVs, strategically timing the use of the whip like kids with PlayStations.

This is a society in the throes of an astonishing and dynamic modernisation over the past 10 years. The skyline in Doha has been forested with vast skyscrapers, each of them striking and often beautiful. They are building new cities on reclaimed land and they are sucking in the sea water, removing the salt and cultivating avenues of trees. Their airport has just run out of room, and they aren’t faffing around with some study into the options – they are building a new one, right on the sea.

They are solving their traffic problems with a brand new metro, and already they have spanking new university campuses, with world-class medical faculties, and their eerily lovely museums are being filled with the treasures of the Earth.

The opportunities for Britain are enormous. But for one reason or another, the last Labour government made the mistake of not paying enough attention to this part of the world.

Tony Blair never visited Qatar once, even though it was a British protectorate until 1971. Well, we are making up for that now. I went to the British Embassy party for the Queen’s birthday on Saturday night, and I swear your heart would have burst with pride. There were 1,800 happy people there, most of them Brits, and most of them involved in a surge of UK exports to the Gulf.

The Qataris are wearing M&S underwear beneath their kanduras. They are eating in Gordon Ramsay’s restaurants. They are driving Land Rovers and phoning with Vodafone – and last year the UK exported goods worth a record £1.3 billion to Qatar alone; not bad for a place with only 1.8 million people. It was a joy to hear the natives speak spontaneously of their affection for Britain. I lost count of the number of times I was told: “London is my second home.”

They know the UK capital like the back of their hand; they want to invest even more. Not just in the top-end luxury brands, but in infrastructure and affordable homes, such as the Qatari investment in the Olympic Park. There is so much we can offer, so many ways to build on this partnership. Qatar will host the World Cup in 2022 and they may need our expertise in keeping such a big project to a timescale and on budget.

They want to collaborate on higher education, on culture, on medicine, on science. They want to diversify away from hydrocarbon, and we should be first in the queue to help. I was amazed at the boom in the Gulf, for it is so very different from our wretched European story. For five years the crisis has dragged on, and every time we’ve thought the UK might attain an escape velocity, the euro has had another convulsion and confidence has drained away.

Today, the Gulf is doing well because of resurgent demand from Asia, and above all from China. America is returning to life, too – and as to our continent, well, Europe is a microclimate of gloom. I came away from a week of talking to hundreds of businessmen and political leaders in the Middle East, and I am more convinced than ever that the world has changed profoundly since 2008, and that the pace of change is accelerating.

Since the crisis began, “emerging markets” have provided the growth in the world – at least two thirds of it. Of course Europe will always be vital and we will always have a colossal stake in America. But it is in Asia, the Middle East, Latin America and Africa that we must expand our businesses and restore our instinct as a great trading nation.

It is an extraordinary fact that it is now the Commonwealth countries, so long neglected by the UK, that are turning into the powerhouses of the future. We have more friends than we sometimes imagine.

She was the greatest Prime Minister since Winston Churchill, we say – and the comparison is apt, because she was as brave as Churchill; indeed, you could argue that she was even more combative than the wartime leader, more willing to pick a fight on a matter of principle.

First I remember the horror of the IRA hunger strikes, and my teenage disbelief that the government of this country would actually let people starve themselves to death. But I also remember thinking that there was a principle at stake – that peace-loving people should not give in to terrorists – and whatever you thought of Margaret Thatcher’s handling of the tragedy, you could not fault her for consistency.

Then I remember watching that Task Force head for the Falklands, when I was doing my A-levels, and thinking the whole thing looked mad. The islands were thousands of miles away and seemed to be mainly occupied by sheep. The Americans weren’t backing us with any particular enthusiasm, and the BBC was endlessly burbling on about some “Peruvian” peace plan, under which we would basically accede to the larceny of Argentina.

I could see that the Prime Minister’s position was desperate; and yet I could also see that she was right. She was sticking up for a principle – the self-determination of the Falkland Islanders; and I remember a sudden surge of admiration.

And when Arthur Scargill and the miners tried to unseat her in her second term, I remember the other students passing the bucket round in the Junior Common Room. I thought about it, since I could imagine that things were tough for communities where coal had been a way of life for generations. I could see how it would eat away at your self-esteem to be told that your labour was no longer necessary.

Then I reflected on what was really going on, and the way Scargill was holding a strike without a proper ballot, and the fundamental dishonesty of pretending that there was an economic future for coal. I suddenly got irritated with my right-on student colleagues, and was conscious that some kind of line had been crossed.

I was now a Thatcherite, in the sense that I believed she was right and the “Wets” were wrong; and I could see that there was no middle way. You either stuck by your principles or you didn’t. You either gave in to the hunger strikers, or you showed a grim and ultimately brutal resolve. You either accepted an Argentine victory or else you defeated Galtieri.

You either took on the miners or else you surrendered to Marxist agitators who wanted to bring down the elected government of the country. You either stuck by America, and allowed the stationing of missiles in Europe, or else you gave in to the blackmail of a sinister and tyrannical Soviet regime.

That was what was so electric about Margaret Thatcher, and that was why I found myself backing her in her last great battle, over Europe. Once again, it was a matter of principle.

The first time I found myself in her presence was at the Madrid EEC summit in 1989, which I reported on for this paper. I remember distinctly how she bustled into a packed and steaming press room – brushing right past me. “Phwof,” she said, or something like that, as if to express her general view of the Spanish arrangements.

It struck me then that she was much prettier than I had expected, in an English rose kind of way. I also thought she seemed in a bad mood. She was. As we were later to discover, she had just been ambushed by two very clever men – Nigel Lawson and Geoffrey Howe – and told that she must join some European currency project called the Exchange Rate Mechanism. She resisted, and they had threatened to resign.

She objected to their proposals, because she didn’t believe you could solve the country’s economic problems by trying to align sterling with other currencies in a kind of semi-straitjacket. “You can’t buck the market,” she said, and she was proved resoundingly right. The ERM turned out to be a disaster, and the British economy only started to recover when the pound crashed out on September 16 1992.

She was right not just about the ERM, but about the euro itself. She was virtually alone among all European leaders in having the guts to say publicly what many of them privately agreed – that it was courting disaster to try to jam different economies into a currency union, when there was no political union to take the strain.

Look at the unemployment rates in Greece and Spain, look at what is happening in Cyprus, and the sputtering growth of the eurozone. It is impossible to deny that she has been vindicated – and she was right because she took a stand on principle: that it was deeply anti-democratic to try to take crucial economic decisions without proper popular consent.

I cannot think of any other modern leader who has been so fierce in sticking up for her core beliefs, and that is why she speaks so powerfully to every politician in Britain today, and why we are all in her shade. In the end she was martyred by lesser men who were fearful for their seats.

But by the time she left office she had inspired millions of people – and especially women – that you could genuinely change things; that no matter where you came from you could kick down the door of the stuffy, male-dominated club and bring new ideas. She mobilised millions of people to take charge of their economic destiny, and unleashed confidence and a spirit of enterprise.

She changed this country’s view of itself, and exploded the myth of decline. She changed the Tory Party, she changed the Labour Party, and she transformed the country she led: not by compromise, but by an iron resolve.