The success of British Prime Minister David Cameron’s flagship immigration policy was called into serious question yesterday, dealing him a potential blow ahead of 2015 elections by playing into the hands of a populist anti-immigration party.

A report by lawmakers from across the political spectrum concluded that Britain’s migration statistics were grossly unreliable and “not fit” for purpose, undermining the credibility of Cameron’s assertions about the issue.

Immigration is a hot button issue in Britain, where Cameron is trying to stop an exodus of voters to the UK Independence Party (UKIP) before a parliamentary election in two years’ time, and polls show the issue is one that worries voters the most.

Concerns have been fuelled by warnings in the right-leaning press about “hordes” of Romanians and Bulgarians moving to Britain next year when EU freedom of movement restrictions lapse, at a time when Britons face rising competition for jobs.

To compound Cameron’s problems on immigration, a government pilot scheme that involves vans driving around London with billboards telling illegal immigrants to “go home or face arrest” has angered his junior coalition partner, the Liberal Democrats, and prompted allegations of racism.

Questioning immigration was for years regarded as racist in Britain, but all three main parties have started to talk tough about the subject in response to rising public anxiety, campaigns in the country’s popular tabloid press, and the popularity of the anti-immigration UKIP.