Leading article: Incredible capping

There was always a suspicion of sleight of hand about the Conservative Party's policy on immigration during the election campaign. The public are clearly exercised about the number of immigrants who have come to Britain over the past decade. So during the general election campaign, the Tories made populist noises on the subject to win votes. But the stereotype of immigrants to which the public most object – Eastern European scroungers begging in the streets – are a class of immigrant beyond the control of any British government, of whatever party. Citizens of the European Union are entitled to free movement within member states and there is nothing even the most right-wing administration can do about that, short of leaving the EU.

So the Home Secretary, Theresa May, in order to live up to her party's election promises, was yesterday forced to announce a cap on the number of non-EU migrants entering the country. She claimed that these represent a majority of incomers – 52 per cent – though reliable sources suggest that the figure is a mere tenth of that. Ms May, who got herself in a bit of a muddle over the difference between net and gross figures, was unpersuasive on this. What is more credible is the concern from business leaders that the curb will undermine the Conservative proclamation that Britain is "open for business". Ms May is planning a 5 per cent cut in Tier One of Britain's points-based immigration system, which includes highly skilled migrants, entrepreneurs and investors; she also wants a similar cut in Tier Two workers, who include skilled migrants with job offers. Exempting individuals, like top footballers, may keep the populist press off the government's back, but it will risk depriving global industries of the skills they need, harm universities' incomes from foreign students and sit ill with William Hague's foreign policy strategy of building links with rising powers like Brazil and India.

Ms May's coalition partners, the Lib Dems – who in other circumstances might have been expected to insist that immigration is in fact good for the UK – have fallen shamefully silent. But the truth is that migrant workers, though they can put a heavy burden on public services in places, on balance contribute far more to the British economy than they take. Figures from George Osborne's new Office for Budget Responsibility suggest that a fall in immigration could reduce the UK's GDP growth by as much as one per cent a year by the end of this parliament. Whichever way one looks at this policy, it simply does not add up.