Deborah Orr: How ruthlessly is Britain prepared to battle with those who want a slice of its wealth?

The vast movement of people across borders is a defining feature of globalisation. So it is hardly surprising that, as a new cross-party report on the subject from the House of Lords repeats, immigration to Britain "has reached a scale unprecedented in our history". The general tenor of the report implies, as does broader national debate around the issue, that the influx is merely the result of recent liberal border and immigration policy in Britain. A cap on immigration from outside the EU is all that is needed to roll back the tide, or, as Gordon Brown maintains, just a rigorous new points system, delivering similar but less crude restrictions.

The two are simple arguments, and underlying them both is the suggestion that, somehow, Britain can, and ought to, expect to remain untouched – or at least no more touched than it already has been – as the world convulses and changes around it. The real questions, however, are not whether Britain can actually avoid change, but how long it can do so, and how ruthlessly it is prepared to do battle with the masses of people in the world who want just a little a slice of its wealth.

Britain is by no means the only country in the world that has "lost control of its borders". Globally, figures on the mass movement of populations are hard to come by. But it is estimated by the UN that there are presently about 200m migrants in the world, or three per cent of the world's population, double the number that there were in 1980. These figures make the numbers that Britain is wringing its hands about – a net yearly immigration of 190,000 since nine new countries joined the EU in 2004 – look marvellously puny.

In the most general of terms though, it is not the counting of who is moving where, across national borders, that makes clearest the terrifying unsustainability of world migration movements. The most obviously problematic migration is from the countryside to the city. Again, the figures are uncertain. But it is a fair bet that already the world's urban population outnumbers its rural population. This, as Mike Davies says in his clotted, depressing, important book, Planet of Slums, "is a watershed in human history, comparable to the Neolithic or industrial revolutions."

The most perilous aspect of this vast resettlement is that it has become uncoupled from economics. People are flowing from the countryside into the cities in search of urban futures that are not there. In the developing world "urbanisation has been disconnected from industrialisation, and even from economic growth". A quarter of city dwellers live in absolute poverty, surviving on less than a dollar a day. An influx of humans that we do not have the resources to look after, is what we fret about in Britain. And no wonder. The hopeless consequences of such population movement are already starkly plain to see.

In this context, the assertion of the cross-party report that immigration has neither improved nor damaged the economy, is still positive news, even though it blasts a politically useful hole in the government's claims about the economic benefits of immigration. Only the most cock-eyed "open borders" optimist would now assert that mass migration was not placing some pressure on British public services and housing. The points system, with its "social fund" is the present government's own practical admission that the difficulty is real. Nevertheless, as far as global trends are concerned, we don't know that we are born.

Not that any British politician would find it useful to go out on the stump, citing "global context" as a vote-catcher. Labour has long stood accused of having deserted its heartland supporters, and it cannot afford to ignore an element of drift away from Labour among some voters, and towards the British National Party. It cannot afford to ignore either, the delight with which Conservatives have seized upon promises made by the report's chair Lord Wakeham, that a future goal, achievable via firm control on immigration, must be the driving up of low-end wages, and a robust policing of employers who are abusing the employment laws. "British jobs for British workers", I think it's called.

This latter, of course, is just one tiny example of the almost comic dissolution of what used to be called "party lines". Labour is being excoriated for its fulsome embrace of global neo-liberalism by a conservative party that gleefully answers the trades unionist's call for ordinary people to be protected from its consequences. It's quite a sight. Again, though, keeping the "informal economy" at bay is easier said than done, whatever your political stripe.

In Britain, we still enjoy debating our class system, and its odd nuances. It remains one of our favourite parlour games. Worldwide though, one thing is not up for debate. The global informal working class, without legal recognition or rights, says Mike Davis, " is about one billion strong, making it the fastest-growing, and most unprecedented, social class on earth". When we talk fearfully of "economic migrants", it is this mass of seething desperation that we fear most.

From early on, the Government was criticised roundly for its inability to tell the difference between "genuine asylum-seekers" and "economic migrants". The government responded to its critics by concentrating on making the process of seeking asylum in Britain as draconian as was possible. It has succeeded.

A report just as critical of government policy on immigration, published last week, was seized on far less enthusiastically by the Conservative Party, even though its contents were ever bit as instructive. That one denounced Labour's treatment of asylum seekers, suggesting that imprisonment without trial, even of children, the deployment of violence in the execution of deportation, even against children, and the use of destitution as a weapon, even against children, were tactics not worthy of a civilised nation.

The government was stung by the criticism, brushing it aside in a proud boast about its effectiveness in bringing down asylum applications. What is not known, and what the government admits it doesn't know, is whether the drop in applications simply indicates a drop in numbers seeking formal recognition in Britain. The high proportion of people claiming asylum with dependent children suggests to me that the asylum process is now most attractive to people who have difficulty in joining our own informal economy. They are the only people vulnerable enough to volunteer to be kicked out.

Lord Wakeham's report accepts that Britain's asylum policy is strict enough already (how could it be more strict, after all), and also accepts that open borders within in the EU are a fact of life. Its beef with Labour is over whether a yearly limit in immigration should be set. Labour says their restrictions on the quality of the folk who can come here will keep numbers down enough. Both parties, however, continue to promote globalisation, while ignoring John Donne. He told us back in the Jacobean period that "no man is an island, entire of itself." What politician cares to admit that no island can be an island for too much longer either?

d.orr@independent.co.uk