ONCE IT'S gone, it's gone. It became clear last week that the half-century-long consensus over immigration has finally collapsed under the weight of political incompetence. The era in which liberals would automatically support inward migration, come what may, has ended. And it is now possible to speak about limiting it without being accused of racism.

The government's inability to get its numbers right last week was the last straw. In the space of hours, the number of migrant workers since 1997 went from 800,000, to 1.1 million to 1.5m - half of all new jobs created in the last decade. No wonder the government failed to provide funds for education, housing and social services - it didn't have a clue how many more people would be using them. If you can't measure it, you can't manage it.

Clearly, the government simply lost control, and by so doing it has seriously damaged the case for free borders. Inward migration can only be justified if it does not harm the host population; yet hardship has undoubtedly been caused to British citizens and immigrants alike. But the greatest damage has been to opinion. The political initiative has been handed to the right, whose warnings about immigration now seem vindicated.

Even Gordon Brown has taken to using a slogan that belonged to the British National Party (BNP) in the 1980s: "British jobs for British workers". His call for a racial dimension to employment policy - in his first Labour conference speech as leader - marked a turning point in British politics. Nothing like it had ever been heard from anyone on the left before. It also marked a new benchmark for political hypocrisy, since it was the former chancellor's economic policies above all that caused the crisis.

Now, I know immigration isn't a crisis - that most of the recent migrants from eastern European countries like Poland will probably go back; that the NHS couldn't do without them; and many of the rest are students who are paying us a lot of money. Without immigrants, the British economy would collapse.

However, English public opinion has taken a decisive turn against migrants, and political parties, led by the Tories, are responding. David Cameron is talking about a cap on immigrant numbers to below 200,000 a year. It can only be a matter of time before Brown follows suit. Liam Byrne, the immigration minister, has refused to rule out introducing annual quotas on non-EU migrants.

Now, I say this is a change in English opinion not because I believe Scots are incapable of being anti-foreigner - in fact, polls have suggested that many Scots are profoundly racist. But the issue is different in Scotland, because there is relatively little immigration here and it has mostly been white. I'm sorry to mention skin colour, but the fact remains it is the most visible manifestation of migration.

Moreover, in Scotland there is no political party on the right to make a fuss, since the Tories are a marginal force. The SNP do their utmost not to be like the many European nationalist parties, such as the Belgian Vlaams Blok, which have been hostile to immigrants. Finally, Scotland has had a demographic deficit, with a falling, ageing population. The young Poles have come to the rescue.

So this is very much an English crisis. The immigration debate has turned on its axis, partly because of the emergence of terrorist groups such as the London bombers in cities such as Leeds, and partly because of the strain mass immigration has put on stretched infrastructure. The fact most recent migrants are white is another reason people are being more open on the issue; talking about cutting the numbers of white people coming here doesn't sound racist.

BUT people have had enough. They resent the way their cities seem to have taken on the character of another country. They object that large immigrant families are being housed while they remain hopelessly on council waiting lists. And they complain that nobody can afford to buy a house because much of the affordable stock has been bought by buy-to-let landlords to rent out at exorbitant rates to immigrants, legal or illegal.

We don't know how much of this is true of course, and the Commission for Racial Equality is to mount a proper study into whether immigration is "crowding out" the British population. But the perception is clear - and nobody seriously denies that the housing crisis has been aggravated by immigration.

In southern England, workers face a double whammy: they are undercut at work by non-unionised immigrant labour, then find they can't afford to buy a home. No wonder they feel resentment. The English working class has shown remarkable tolerance in the circumstances. Imagine if Polish politicians were coming here and doing the job of MPs for half the money - immigration would be halted overnight.

Yet there has been remarkably little overt racism in recent years, despite the presence of a well-organised BNP and a popular press that rarely misses an opportunity to whip up scares about asylum and illegal immigrants.

But their patience isn't inexhaustible. People feel they have been lied to - and they have. Remember how we were told only 13,000 immigrants would come here after the enlargement of the EU in 2004? The true figure was around 400,000.

Governments don't make mistakes like that by accident. The truth is that Gordon Brown wanted immigration by stealth because he wanted to keep wages down during the long boom. He just didn't want anyone to know about it.

But where do we go from here? Now the consensus on immigration is undermined, what is going to happen in the city centres? Well, I think we are still a long way from race riots, but unless this government gets its act together things are going to get tense. In the end, if people don't want their communities changed by uncontrolled immigration, that is their democratic right.

The only way to resolve this is for the government to start being honest, and return to policies that boost social capital: more houses, council and private; an end to tax breaks for buy-to-let; stronger unions; better education of immigrants; an end to casualised work. In the past decade, the wealthy have done well out of cheap plumbers, nannies and high house prices. It's time they put something back.