The last Roman ruler to persecute Christians, Diocletian brought stability to the empire after the chaotic third century. In 301AD, he passed his edict on prices, an unsuccessful attempt to stop inflation by imposing maximum prices on common goods.

Most contentiously the rules are proposed to apply to the staff of European banks who work outside the EU, in financial centres including New York and Singapore.

Supporters of the cap say it will discourage bankers from pursuing the sort of high-risk deals that helped cause the financial crisis. Opponents point out that hedge funds, private equity companies and other financial firms are unaffected.

Mr Johnson said the rules would only harm Europe.

“Brussels cannot control the global market for banking talent. Brussels cannot set pay for bankers around the world,” he said.

“The most this measure can hope to achieve is a boost for Zurich and Singapore and New York at the expense of a struggling EU.” Mr Johnson added: “People will wonder why we stay in the EU if it persists in such transparently self-defeating policies.”

Britain had attempted to block the rules, but was outvoted. Ministers can now only argue about how the cap should be applied.

Mr Cameron said on Thursday that Britain would push for more flexibility in the cap.

And so it went on, all the time I was with her. I would stand there tongue-tied, while she showed that she had thought about people’s problems and in many cases actually done some work to solve them.

She struck me as someone who deserves to win on that basis alone; but I want her to win because she is not some cookie-cutter candidate from Central Office. She does not have a pasteurised and homogenised set of metropolitan opinions – indeed, some of her opinions are thought to be a bit out of step with the party leadership. But isn’t that what we want these days?

I would much rather have Maria Hutchings than some utterly Janus-faced and hypocritical Lib Dem, telling one set of electors one thing and then doing the exact opposite to someone else. Down in Eastleigh, the Lib Dems are in total charge of the council, and have just decided to build 1,400 homes on green space; and yet Nick Clegg has the bare-faced cheek to say that his party is all about resisting development in the countryside.

That is the trouble with this yellow albatross that is currently around the Tory neck: they are much better at the politics of opposition than they are at government. It is all very easy telling the students of Britain that Lib Dems are opposed to tuition fees, but when you get to power you have to work out a way to finance higher education. That is why Clegg’s most famous contribution to UK politics will remain his smash hit, I’m Sorry, as seen on YouTube a couple of million times.

In the same way, the Lib Dems have spent the past 10 years going around telling everyone, in their soothing and self-righteous way, that you don’t need nuclear power, and you don’t need coal power, and you don’t need gas power – all you need is a few wind farms. Now they are in office, they are discovering that their so-called energy policies will have us all reading by candlelight.

So I hope the good people of Eastleigh will go for Maria, and not these wobbling Lib Dem tergiversators. And if, by the way, you are thinking of voting for Ukip, can I just point out that Nigel Farage is a thoroughly amiable fellow to have a pint with, and all the rest of it; but a vote for Ukip is effectively a vote for the Lib Dems, since they are the only ones who can beat Maria and the Tories.

And that means a vote for Ukip is tantamount to supporting the party that is most boneheadedly and full-heartedly Europhiliac, the Lib Dems – the party that actually opposes any kind of referendum at all, let alone the in/out vote that David Cameron is offering the country (despite them promising precisely such a vote in their manifesto).

The final reason for giving my total support to Maria Hutchings, mother of four and candidate extraordinaire, is that she is doing spectacularly well in keeping the Tory end up, when you consider that this is the deepest and grimmest of mid-terms.

It was only a few weeks ago that serious Labour commentators were saying that the party should on no account write off Eastleigh. The seat was there to be won, they said, and on the face of it that was right. Look at the demographics, and it is a straight Labour/Tory marginal; and indeed, the Labour Party came second in 1994.

But where is Labour today? I don’t think I saw a single poster or piece of political propaganda advertising the main opposition party – the one that is meant to be contemplating government in 2015. Miliband’s troops are non-existent in an area that Tony Blair’s team would have fought hard to possess.

I don’t blame their candidate, an engaging gag writer from Have I Got News For You. Labour’s failure to make an impact is a biting comment on Ed Miliband, and his vacuous prospectus for the people of this country.

Whatever happens on Thursday, it will be a victory for the Coalition that the Conservatives lead, and a defeat for Miliband; and if Maria Hutchings pulls it off – the first Conservative by-election victory, in government, for more than 30 years – it will be stupendous.

They are bringing a judicial review and Dr Davidson is hoping Transport for London (TfL) will be forced to accept the advertisements.

They argue that other advertising campaigns – including Stonewall’s, and campaigns for underwear – have been allowed TfL.

“This is all about being free to talk about these issues,” said Dr Davidson, who himself has a homosexual past, but has been attracted controversy for suggesting gays can become heterosexual through counselling and prayer.

“It was a mistake to assume these views we were expressing came from entrenched homophobia, and failed to recognise that people who want to walk away from their homosexual feelings are a group in their own right.”

He has instructed Paul Diamond, the human rights barrister, in this week’s case.

Stifling debate by banning their advert amounted to discrimination, the trust will argue.

They will point in particular to one poster which some Christians found offensive. Funded by Richard Dawkins, the academic, and the British Humanist Association in 2009, it said: “There’s probably no God. Now stop worrying. And enjoy your life.”

Andrea Williams, director of the Christian Legal Centre, which is supporting Dr Davidson’s case, said: “The ban on these advertisements was the beginning of a kind of reverse discrimination which threatens to obliterate debate in the public sphere.

“Boris Johnson needs to realise his mistake and ensure there is freedom for all in the marketplace of ideas. He cannot prefer one group over another.”

A Transport for London spokesman said: “The advertisement breached TfL’s advertising policy as in our view it contained a publicly controversial message and was likely to cause widespread offence to members of the public.”

The Prime Minister, a champion of minimum alcohol pricing, has insisted this “wouldn’t really affect family budgets, but would deal with this problem of very aggressive deep discounting and some binge drinking”.

However, he is facing opposition over the plans from a number of senior Tories, who fear it will hit moderate middle-class drinkers with higher prices. Some Liberal Democrats also see the plan as “illiberal”.

There are also fears it could run into legal difficulties with the European Commission, which has raised concerns about Scotland’s plans to introduce similar measures.

The Home Office is still officially consulting on the plans but the Government appears to have been slightly cooling on the idea, amid persistent worries about the cost of living.

Even though Mr Cameron has publicly backed the policy, it is still possible that the price per unit could be revised downwards or scrapped entirely and replaced with voluntary agreements with industry.

Miles Beale, chief executive of the Wine and Spirit Trade Association, said the Mayor is right to point out problems with the plans.

“Under the Government’s plans to set higher alcohol prices through minimum unit pricing it will be the majority of responsible drinkers who will be asked to pay more,” he said.

“Pushing up prices to deal with the actions of a reckless minority is unfair. Ordinary people looking for value for money in their weekly shop should not be labelled as binge drinkers.”

Research carried out by Sheffield University for the Government has showed that a 45p minimum would reduce the consumption of alcohol by 4.3 per cent, leading to 2,000 fewer deaths and 66,000 hospital admissions after 10 years.

The number of crimes would drop by 24,000 a year as well, the research suggested.

However, the alcohol industry has disputed these findings. A new report by the Centre for Economics and Business Research, commissioned by the industry, claimed the official figures are unreliable and based on old data from 2006 which have already been proved wrong.

The proposed tax is unfair on those who may be asset-rich – the elderly widow springs to mind – but whose income is low. If Labour were to pursue the policy announced last week, and set the threshold at £2 million, the result would be bizarre – from discontinued improvements to deliberate vandalism: anything to help the home owner limbo dance under the danger area. It is peculiar to try to raise money for the state by taxing this one particular form of wealth, and in this one particular way.

What about someone who owns several houses, all of them worth £1.9 million: why should he or she pay nothing, while someone who owns just one pricey home gets totally clobbered? What about someone who lives in a home worth a million, but happens to have a load of Van Goghs and Cézannes on his kitchen wall, or gold bars under his bed? Why should he get away with paying nothing, while the taxman pulverises the little old lady still living in the former family home next door?

The pressure to be fairer between households, and to reduce the sudden severity of the tax, would be very great. If Ed and Ed came to office – a very big if – they would almost certainly modify the mansion tax, so that it was less of a blatant disincentive to doing up a home. They might have several bands for the new tax – hundreds of bands, thousand of bands (or Milibands, as they will be known).

They might decide to solve the elderly widow problem by going with the even more demented Liberal Democrat proposal, and taxing fixed wealth of all kinds. So we would have a new race of ghastly beady-eyed officials tasked with feeling under our beds for gold bars and running an expert eye over the pictures on the wall, or rifling through the jewellery box. An Englishman’s home, to put it mildly, would no longer be his castle.

Every property owner in the country would be engaged in an undignified haggle with the authorities to persuade them that their home was under this or that threshold. The end result would be in many cases to force sales, and to reduce the value of property – and for a country whose wealth is, for better or worse, so tightly tied to property, that would not be a good outcome.

Yes, of course we need people to be able to afford to live in Britain. But the answer is not to make it even more punishing to own a home in an expensive part of the country. The answer is to get going with a massive programme of house-building on the many brownfield sites. Here in London we have a crying need for homes — hundreds of thousands of them over the next 10 years.

We could build about 80 per cent of them on the 18 brownfield opportunity areas that have already been identified across the city, and all we need is a steady stream of funding to be able to get on with it. That could be found by simply earmarking, for London, the £1.3 billion that the London residential market already raises in stamp duty. And with one in four small and medium businesses in construction, that programme would get huge numbers of people into work.

If you listen to Nick Boles, the housing minister, you can see that he understands the urgency of the problem. The Treasury understand it, and George Osborne knows that Tories win elections when they help aspirant people get the homes they need – and it is time to return to the great Tory building programmes of the Fifties, but with beautiful standards and on brownfield sites.

As for Labour, they have shown their true colours. The Blairites in the party must be watching with incredulity and despair. Never mind the individual injustices – the message of the Miliband policy is that Labour is once again hostile to one of the deepest instincts of the British people: to show the energy, enterprise and ambition to want to improve your own home and to raise its value. I cannot believe Miliband will pursue this policy through to the election. If he does, he will have signed his political death warrant.

You fill your electronic notebook with all kinds of exotic detail and all the while you are analysing the mystery. Why does one culture ban the eating of an animal that another culture regards as top nosh? What is it all about?

You chew the end of your intergalactic pencil and then boing – your eyeballs come out on foot-long red stalks as inspiration strikes. It’s all about control. This amusing species called Homo sapiens has only lately emerged from prehistoric savagery; and what the human race fears most is a return to that darkness and disorder. So over the millennia the human race evolved the idea of taboo, as a way of creating social cohesion.

Things were deemed to be nefastus, haram, forbidden. Individually and collectively, people developed little electric fences in the mind, and by agreeing on what was taboo they defined themselves; they defined themselves in opposition to others; and they helped to create a crucial sense of identity. By controlling small aspects of behaviour, society helped to control the big ones.

Taboo, you conclude, was important in the creation of order. With growing excitement you continue your researches, and you observe several characteristics of taboos. They may become detached from their original rationale – shellfish and pork are less likely to give you food poisoning these days – and yet still have great force.

Taboos are psychologically powerful since they affect inescapable features of human experience: diet, reproduction, sexual behaviour, menstruation, defecation and so on. You note that taboos are often accompanied by a great deal of hypocrisy. Various sexual practices denounced as unthinkable turn out to be fairly common, and as for eating horses – well, you have to wonder whether the British were really as naive as the newspapers make out. Surely, you ask yourself, people must have thought there was something a bit dodgy about the meat in a fairground hamburger; and surely they must have wondered about the export of all those British ponies to foreign abattoirs. Where did Shergar go?

But if they suspected they were eating horse, they didn’t mention it. It was taboo. The most interesting feature of the taboo, you discover, is the way it mutates over time. Things that were acceptable can become outrageous – and vice versa. Smoking is out, and will never come back in. I have been reading Herzog, the 1964 novel by the Nobel prizewinner Saul Bellow, and was struck by the way he refers to “negroes” – a term that would almost certainly preclude him from being read aloud on Radio 4 today.

Or take the issue of gay marriage. If the polls are correct, most people just can’t understand what all the fuss is about, because the taboo on homosexuality has gone – and seems to have been transmuted into a much more virulent taboo against any kind of underage sex. With assumptions changing so fast, it is no wonder that some people feel angry and bewildered. They aren’t bigots; they’ve just been marooned by the fluctuating tides of taboo.

As you get back into your spaceship, you draw several conclusions for the paper on human taboo that you will present to your fellow Martian anthropologists. You decide that taboos vary from country to country because in a way it doesn’t matter exactly what the prohibition is: what matters is the fact of the taboo; and the process of agreeing – and changing – the boundaries of acceptable behaviour is central to what makes a society.

Where, you wonder with a final flourish, will taboo go next? If the British and the Americans already regard the eating of dogs, cats and horses as haram, how long before all animals are objects of dietary taboo? In 100 years’ time, you wager, the British public will be paying for memorials for the legions of animals that have died to feed them, and the British prime minister will issue an apology to all oxen that have provided the roast beef of old England.

Of course it will all be nonsense, and people will flout the taboo. But that is not the point. The important thing about taboo is that it should exist.