It is Britain's success that attracts migrants. So do we really want to be less successful?

Migration is more a function of growth than a cause of it. People move where the jobs are

A burden or a boost to the economy? The economic aspects of immigration may play second fiddle to the political ones but they keep being cited in the argument, so they need to be tackled. If inward migration makes the country richer, the people who argue against it have to acknowledge the costs of attempting to restrict it. And, if it makes it poorer, people who argue in favour have to acknowledge the costs.

A burden or a boost to the economy? The economic aspects of immigration may play second fiddle to the political ones but they keep being cited in the argument, so they need to be tackled. If inward migration makes the country richer, the people who argue against it have to acknowledge the costs of attempting to restrict it. And, if it makes it poorer, people who argue in favour have to acknowledge the costs.

The trouble is, we don't really know. There is, as you might expect, a considerable amount of economic research on the subject. The broad outcome of this is that skilled migrants add considerably to an economy, unskilled ones add a bit, and people who do not work (or are, for whatever reason, not allowed to work) and are eligible for benefits, are a net cost to the economy.

There is nothing wrong with this sort of analysis - it is the basis from which any sensible discussion ought to start. But I think we have also to acknowledge that, in a way, the question is phrased the wrong way round. Migration is more a function of economic growth than a cause of it. People move where the jobs are. Scots and Irish emigrated to the US, Canada and Australia in the 19th century because opportunities were few at home and prospects abroad were better. People are now moving back to Ireland because of its great growth spurt - the spurt was caused by changes in taxation and other economic policies, not by the influx of job-seekers, which only happened once the boom was well established.

Much the same happened in Germany after the Second World War. During the early stages of reconstruction there was no pressure from immigration. Then, as the economic miracle took hold, the need increased for workers to man the factories that were pumping out Germany's engineering exports. So Germany became the home for "guest workers", mostly from Turkey.

And now it is happening in Britain. The country is experiencing the strongest growth among the large western European nations. If we are honest, I think we have to admit that the reasons for this are not fully clear. They have something to do with the economic reforms associated with Margaret Thatcher (though some would argue they started under Denis Healey), which created the most flexible of the European economies. They have something to do with the strength of financial services, which had a historic base in London and which have been a huge cash cow for the whole of the economy. They probably have something to do with the growing economic importance of the English language: look around the world and the fastest-growing developed economies are either countries where English is the mother tongue or is widely spoken.

At any rate, whatever the reason, the UK economy seems to be able to grow at about 2.75 per cent a year, maybe a little more. That is fast enough to suck into employment most of the people already here with the skills that are needed, and to provide jobs for a raft of immigrants from places as divergent as Australia, Poland and Nigeria.

Those three countries well illustrate the extraordinary variety of migration patterns. It happens today to be Australia Day and the High Commission is noting it by publishing a new estimate of the Aussie contribution to the UK economy. There are, on average, 370,000 Australians in the UK, Australia's largest expatriate community and one of the largest expatriate communities in Britain. It is a two-way trade. In 2003, more than 800,000 Australians visited Britain and a similar number of Brits visited Australia.

The High Commission notes that Australians have the highest employment rate for London's migrant population: 87 per cent of them are in jobs and 65 per cent have a higher level of qualifications, as opposed to 31 per cent of Londoners in general. They occupy such high-profile positions as the head of British Airways, director of the Royal Ballet School and of the Royal College of Music, and editor of The Times. This crystallises the reason for this migration. These people do not come here for the weather. They come here for the jobs.

Now look at Poland, the largest of the new member states of the European Union and, as such, the largest potential supply of "new" labour from Europe. There is not, as yet, a Polish editor of The Daily Telegraph, though we do have the son of a Romanian migrant as head of the Conservative Party - and Romania will be in the next wave of EU members. Poland has now become the largest new supplier of skilled labour for a number of industries and anecdotally, these people are very welcome. There has been no real evidence of disruption in the labour market, or a flood of job-seekers pushing Brits out of work, or indeed any of the fears voiced ahead of EU enlargement being realised. Like the Australians, the Poles come for the jobs - and self-regulate the supply of their labour to fit the opportunities available.

In the case of Nigeria, much the same process happens. Nigeria is, in terms of population, the largest country in Africa and Africa is the largest single supplier of migrants. The jobs Nigerians go into at the moment are still of lower profile than those Australians noted above, but the skill levels are high and there is plenty of demand in the labour market for these skills.

Now, of course, everything is not perfect. Any group of people arriving in a different country will give rise to social strains. And some migrants will seek to exploit the welfare services available. There have been job-related tragedies, the cockle-diggers of Morecambe Bay, for example. The fact that the authorities have mishandled migration has made what would always be a difficult situation worse.

But these problems are mostly, not entirely, a function of mishandling the strains of economic success. Any period of rapid growth creates social and environmental pressure: what we are seeing now is nothing compared with the pressures of the 19th century. The question is how to cope better with those pressures.

It may be that Britain's big growth-run is coming to an end which would reduce the pressure for people to come here. Some would still want to do so, of course. But the sense of pressure, which is the thing that alarms the politicians, would be much less.

On the other hand, we may go on being successful in generating low-inflation, solid growth. If that is so, the UK will carry on creating job opportunities for migrants. Migration is a key factor holding down wage pressures - if there were fewer migrants, there would be more inflation and probably higher interest rates. We could try to pull up the drawbridge but, given the performance to date, that would probably result in keeping the people the economy needed out and letting the ones it didn't need in.

Maybe that is too cynical. But it is not cynical to say that if the UK is to remain a vibrant economy, it is inevitable that it will attract job-seekers from the world over. Do we really want to be less successful?