Britain on Tuesday closed the door on most Romanian and Bulgarian workers for at least another year, as the government battled to restore confidence in an increasingly shambolic immigration policy.

As Liam Byrne, immigration minister, announced he would keep tight controls on migrant workers from the two Balkan countries until at least the end of 2008, ministers conceded there were 300,000 more foreign workers in the UK than official figures had suggested. And confusion deepened further as senior MPs claimed the true total could top 1.5m.

In a damage limitation exercise, Jacqui Smith, home secretary, became the latest minister to apologise after government claims that there were 800,000 foreign workers in Britain turned out to be wrong.

Earlier, Peter Hain, work and pensions secretary, wrote to his Conservative and Liberal Democrat counterparts admitting that incorrect figures were given in the Commons while insisting that the revised figure of 1.1m was the most robust estimate available.

However, Frank Field, one of the Labour MPs who was given the incorrect figures, on Tuesday said the latest statistics still lacked credibility, and that the real figure could be as high as 1.6m. The Tories claimed the true figure was 1.5m.

The Department for Work and Pensions on Tuesday night insisted that it was sticking to its revised figure of 1.1m more foreign nationals taking up work in the UK since 1997. It said the 1.5m figure included 400,000 foreigners who had become British citizens and had British passports, some obtained through marriage.

Mr Field said that, while he was not accusing ministers of deliberately falsifying figures, he had criticised them in the past for failing to ensure that figures were accurate. “What we had was a rotten system of statistics that were delivered to ministers, and policy made on these figures. That is what is so alarming,” he said.

According to the MP, ministers had in recent years dodged the issue of population and immigration statistics, fearing that a more robust system would underline policy failures in dealing with the pressures put on housing and social services by population growth and migration.

Chris Grayling, shadow pensions secretary, said: “They are either covering their tracks or they are just not competent.”

“Something felt wrong about these figures. We just asked the questions that Peter Hain should have been asking himself. There is a sense that the whole thing is running out of control.”

Britain was one of only a handful of western European countries to open their labour markets fully to the eight former communist countries that joined the EU in 2004. But the government was completely unprepared for the scale of immigration that followed.

Bulgarian and Romanian workers will only be allowed to work in the UK if they are among an elite of highly qualified staff, part of a quota of agricultural workers, or granted work permits when jobs cannot be filled locally. Finland and Sweden are the only nations in the “old” 15-country EU to have fully opened their labour markets to the two new members.

The Conservatives have a clear five-point lead over Labour, according to a Guardian/ICM poll published on Wednesday. Support for Labour has fallen to 35 per cent, down three points on last month and its lowest level in any ICM survey conducted since Tony Blair left office.

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