Just six months after the government's last crackdown on "benefit tourism", David Cameron has launched another. In an article for the Telegraph, he announces that the period of time EU migrants can claim welfare payments for will be reduced from six months to three (after an initial three-month waiting period). He writes:

We’re also making sure people come for the right reasons – which has meant addressing the magnetic pull of Britain’s benefits system. We changed the rules so that no one can come to this country and expect to get out-of-work benefits immediately; they must wait at least three months. And we are announcing today that we are cutting the time people can claim these benefits for. It used to be that European arrivals could claim Jobseeker’s Allowance or child benefit for a maximum of six months before their benefits would be cut off, unless they had very clear job prospects. I can tell Telegraph readers today that we will be reducing that cut-off point to three months, saying very clearly: you cannot expect to come to Britain and get something for nothing.

The move is not a response to a policy problem (a recent study by the EU Commission found that"so-called benefit tourism" is "neither widespread nor systematic") but a Crosby-inspired attempt to respond to public anxiety over immigration and to neutralise the threat from Ukip.

It is doubtful, however, that it will do anything to help the Tories. By devoting more time to this issue, Cameron is fuelling the perception that immigrants are benefit-hungry wastrels (weren't they meant to be taking "all our jobs"?) while responding with measures that most will regard as inadequate. If welfare tourism is such a problem why not stop migrants from claiming benefits at all? Indeed, why not shut the door to them entirely? The latter option, of course, is not available to Cameron due to the EU principle of the free movement of labour, which is precisely why he is doing his party no favours by raising the salience of this issue.

Rather than perpetuating public fear over immigration, to the benefit of Ukip alone, the PM would be better off telling voters the truth: that migrants are less likely than British citizens to claim benefits and that they contribute more in taxes than they extract in welfare. An OECD report last year, for instance, found that they make a net contribution of 1.02 per cent of GDP or £16.3bn to the UK, since they are younger and more economically active than the population in general.

It's for these reasons that, as the Office for Budget Responsibility has shown, we will need more, not fewer immigrants, if we are to cope with the challenge of an ageing population and the resultant increase in the national debt. Should Britain maintain net migration of around 140,000 a year (a level significantly higher than the government's target of "tens of thousands"), debt will rise to 99 per cent of GDP by 2062-63. But should it reduce net migration to zero, debt will surge to 174 per cent. As the OBR concluded, "[There is] clear evidence that, since migrants tend to be more concentrated in the working-age group relatively to the rest of the population, immigration has a positive effect on the public sector’s debt…higher levels of net inward migration are projected to reduce public sector net debt as a share of GDP over the long term relative to the levels it would otherwise reach."

One might expect a fiscal conservative like Cameron to act on such advice but, as so often in recent times, the PM is determined to put politics before policy. The irony is that, by allowing Ukip to claim yet another victory, he isn't even succeeding in these terms.