Neither David Cameron nor Nigel Farage is likely to mention it, but there is one way to turn back the tide of eastern European migrants lusting, supposedly, for the British way of life.

A gigantic banking collapse and a deep recession are guaranteed to do the trick. On that, at least, the statistics are clear.

As the Migration Observatory at Oxford University has described it, net EU migration to the UK dropped "dramatically" between 2007 and 2008. Meanwhile, for the first time since the mid-1990s, more British citizens were returning to the UK from other European Union countries than were leaving to move to such places. Who would have guessed?

It ought to stand to reason: people migrate to work. They do not come here to sponge from what remains of our welfare state. Benefit tourism, like health tourism, is as close to a myth, statistically, as makes no difference. In October last year, for example, a study by the European Commission found that, where unemployment benefits were concerned, the UK was "the only EU state where there were less beneficiaries among EU migrants (one per cent) than among nationals (four per cent).

Iain Duncan Smith's Department of Work and Pensions has meanwhile discovered fewer than one in 10 benefits applications by people of eastern European origin are successful. The Centre For Research And Analysis Of Migration at University College London says such people are about 60 per cent less likely than British citizens to get benefits or social housing. The idea the UK is a soft touch is pernicious nonsense.

It suits Mr Farage, of course. It certainly suits him better than the self-evident fact people who come to a country to work also contribute to that country. Nor do migrants "cause" low pay in the UK: that would be good old British employers for whom the real soft touch is a UK Government with no interest in legally enforceable standards of decency. The mystery lies elsewhere. If the Ukip leader is talking rubbish, as ever, why does cfMr Cameron follow suit?

As German Chancellor Angela Merkel has said - or allowed to be said on her behalf - the Prime Minister is in danger of talking Britain out of the EU if he insists on picking a fight over the free movement of people. The principle, such as it is, is already hemmed in by dozens of bureaucratic caveats that vary from country to country. No state allows migration without conditions. No one hands out those "lavish" benefits on demand. Yet Mr Cameron persists.

Pandering to those deceived by Ukip involves fresh layers of deceit. It also involves ignoring polling that says the British are not in any great rush to quit the EU, despite Mr Farage and all the Tory back-bench chatter. The UK is not being inundated with migrants from eastern Europe: a Eurostat estimate puts residents born in another EU state at 2.24 million. With all those many European countries to draw on, that is just 3.6 per cent of the total.

There are 1.8m British citizens living in European countries, meanwhile. Some 400,000 of them are drawing UK state pensions; many more take advantage of the social services granted by our partners. Spain alone provides a home for one million of the British people whose rights could be threatened by Mr Cameron's posturing. The right to free movement is not some sort of gift the gullible UK hands out to wily foreigners.

What does Chancellor George Osborne think he means, then, when he says the Government will "always do what is in the interest of our country and our economy"? The economic contribution made by migrants is an established fact. Tory daydreams over still more benefits rules, quotas, a "points-based" immigration system, or limits on the issuance of National Insurance numbers will either require fundamental treaty changes liable to destroy the EU, or, as Mrs Merkel suggests, Britain's departure from it.

Mr Osborne is happy enough to use conditions in Europe as his excuse when his debt and deficit schemes come unstuck. That tale has worn very thin, but its use involves an implicit admission from the Chancellor: EU membership is fundamental to UK trade and therefore to the best interests of this country. To risk that because Mr Cameron has taken fright at Ukip and a section of his own party is utterly parochial.

It also misses the point. Mr Farage is gathering support in England because of myths to do with immigration, not because of the EU. The "immigration issue", equally, has more to do with living standards amid the coalition's austerity programme than with "Brussels", sovereignty, or the number of EU justice measures liable to appeal to the Tory back-benches. If Mr Cameron and Mr Osborne want to solve their Ukip problem they should deal with low pay.

Neither man now shows much interest in the effect of this mess on Scotland, a country still resistant to Mr Farage and still liable to vote to stay in the EU if and when the chance is presented. The Prime Minister might seek to dismiss First Minister-elect Nicola Sturgeon's demand for a Scottish vote, but that hardly ends his difficulties. Not so long ago he and his Chancellor told us an independent Scotland would be cast out of the EU. Now we risk being hustled out because of Ukip. And how would that keep a peripheral kingdom united?

Listen to some of the anti-immigrant rhetoric and you begin to believe that, for some, the facts scarcely matter. Mr Cameron says he will have a definitive view to offer before Christmas, but has maintained freedom of movement will be at "the very heart" of his strategy to renegotiate Britain's relationship with the EU ahead of a referendum. Mrs Merkel, patently aware the Prime Minister is painting himself into a corner, says the right to movement will remain sacrosanct. Then what?

If she is not bluffing - and you can bet she is not - any changes won by Mr Cameron will be wholly cosmetic. If he or his party find that prospect unacceptable then the German Chancellor's logic imposes itself. The old difficulty between Britain and the EU will no longer be concealed. An a la carte membership, one that tries to ignore or overturn the founding principles of the Union, is not available. Why then would the eurosceptic hope of a mere trade relationship on preferential terms be granted on demand?

Those opposed to Scotland's independence have spent a lot of time arguing there are few big or particularly important differences between the constituent parts of the UK. Watch Mr Cameron interpret the national interest in terms of Tory Party tensions and Home Counties politics: you might just be inclined to think otherwise. The Prime Minister has made his priorities perfectly clear.

Some bizarre distortions of logic are involved, in any case, when a Conservative leader supposedly wedded to free trade decries the free movement of labour. The economic case, far less the human one, is supposed to define Mr Cameron's party. But logic, like the UK's EU membership, is heading for the exit.