It was a strange conceit, I thought as I listened to their Laurel and Hardy act on the Today programme yesterday, to suggest that if Nicholas Soames and Frank Field agree on something, then they must be more likely to be right. And I imagine that they conceived that their rectitude was further enhanced by the support of the former Archbishop of Canterbury, Lord Carey of Clifton and the erratic Muslim Labour peer, Lord Ahmed. There they are then, bound together in a new group, Balanced Migration (well, it's hardly going to be called, “Chuck 'em Out” is it?), all their religious and ethnic bases cleared and ready for action. Though why, since they commissioned Migrationwatch UK (aka “Send 'em Back”) to create their platform for them, they didn't just join that organisation, is a bit obscure.

Balanced Migration is so called because it wants to create a rough balance between people going and people coming in. It imagines that by so doing it can limit Britain's population growth to “sustainable” levels, as well as limiting what Mr Field called the transformation of some neighbourhoods “from settled working-class communities to societies they can barely recognise”.

We are left to understand without discussion that such a transformation must, necessarily, be for the worse. The group might as well be called Chuck 'em Out, because its operating assumption is that there will be a huge excess of would-be immigrants over emigrants.

Balanced Migration recognises that employers like to take on migrant labour, but thinks that it can cut the link between people coming here to work, and people becoming citizens, a link that Mr Field described as occurring “invariably”.

I have to say that I would like to see the figures supporting this assertion, but let's move on. What is suggested is that migrant workers (shall we call them gastarbeiter?) be allowed to work here for four years. At the end of that period, if they've proved themselves to be exceptional workers (ie, 20 times as good as indigenous folk) they will be allowed to enter a national lottery for citizenship, which will have 20,000 winners. More, I suppose, if the number of Brits emigrating rises, fewer if it falls. If they either aren't exceptional enough, or don't draw a winning ticket, then they can - let's not beat around this bush, eh? - push off back to where they came from.

This is a hugely unattractive procedure, especially, one would have thought, for a Christian such as Mr Field. Although I suppose that we could always permit a Big Brother type mega-vote on the BBC to follow the lottery draw, with the viewing public deciding a proportion of the winners and losers. It will certainly boost the chances of Goan transsexuals becoming British citizens. But why go through this process at all?

Demographics, ostensibly. Or rather, the crude version of a demographic discussion that the malign influences of Migrationwatch UK, the Daily Mail and government cowardice seem to permit us.

As Mr Field puts it, in less than 25 years the population will grow by seven million, and this will “require building seven new Birminghams”. Incidentally, the unit of apocalyptic population growth varies from organisation to organisation. The barmy Malthusians at the Optimum Population Trust estimate their Armageddon at 57 Lutons, yet others have a problem with Cardiff. The European Commission, Mr Field said, had “predicted that within 50 years Britain would become the most highly populated country in Europe”. Mr Soames brought forward that moment by four decades on the radio yesterday, simply by confusing England with the United Kingdom.

I wonder if Mr Field knows just how unreliable this prediction is? In 1955 government projections assumed a UK population in 1993 of 53 million. The actual figure was 5million more. The reason that the projection was so wrong was that it had not anticipated the baby boom of the 1960s. So for the 1965 projection, now knowing better, the assumption was made that by 2000 there would be a UK population of 75 million. Birth rates fell; the 2000 population was 59 million.

Since 1965 two things have happened to affect long-term population predictions. The most important, numerically, is probably improved life-expectancy rates, and the second is net immigration. But what does this tell us about the future? The statistician Chris Shaw, who wrote a study recently on population forecasting, quoted the American demographer, MichaelS. Teitelbaum as saying that “projecting immigration is impossible, but unavoidable!”. In other words, be careful. We now live in an era of high mobility and rapid demographic change, and - like house prices - what has gone up can come down. For example, the migration assumptions underlying government predictions are that net immigration will plateau out at an annual level above that for any year except 2001 and 2005. In other words, they are very probably too high.

Already about half of those economic migrants who came to Britain from Eastern Europe after 2004 have left. The number of applications for work entries fell by more than 20 per cent between comparable periods in 2007 and 2008. You don't have to be Nostradamus to realise that the coming recession will see that drop further, possibly dramatically. These days even relatively small fluctuations in exchange rates lead to big changes. The predictions, then, are pretty worthless.

This is how the world is, Frank. People, especially young people, brought up with satellite news and the internet, will try to follow their angels and will generally succeed. Read that letter yesterday from the High Mistress of St Paul's Girls' School about how many of her pupils now go on to American universities.

Our 2015 problem may well not be keeping mobile, motivated workers out, but desperately trying to attract them, not least to look after that other unexpected population surge - in the dependent over-80s. The studies are pretty clear: economic migrants bring with them dynamism, innovation and hard work.

Nor are the people that we will need all highly qualified, in the way that the Government's bureaucratic points system seems to assume. But why would many of them, especially workers who, in Mr Field's phrase “do well”, want to face Balanced Migration's insulting lottery? We will lose them to countries that take a more enlightened attitude to globalisation and its challenges.

What should remain is the need for far more flexible planning and a much more plastic idea of the nature of community, because there is no more refuge to be had in demographic protectionism than there is in its economic cousin. Little and Large would make things worse, not better.

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