Gordon Brown was under fire this evening over a series of ‘misleading’ claims about Labour’s record on immigration.

In a highly embarrassing development the independent statistics watchdog, Sir Michael Scholar, has ordered an inquiry into the use of figures supposedly showing that Labour’s new points-based system has reduced the level of immigration.

Mr Brown has also been forced to admit that Labour has not banned low-skilled chefs and care assistants entering the country from abroad, as he has repeatedly claimed during the campaign.

The revelations came as a new study revealed that more than a one million extra immigrants are set to enter Britain over the coming five years.

Shadow Home Secretary Chris Grayling said: ‘This government doesn’t seem to know how to be straight with the public about their record on immigration. ‘For the Prime Minister to be rebuked like this twice is a real sign that he just won’t face up to the consequences of his mismanagement of our immigration system.’

The intervention from Sir Michael came after the Prime Minister used unpublished Home Office figures to suggest that the points-based immigration system had cut the number of migrants from outside the EU.

Mr Brown boasted that the number of IT workers and engineers coming to Britain had been cut by 20,000 following the introduction of the scheme. But he failed to mention accompanying figures showing the number of foreign students rose by 65,000 during the same period.

In a further blow to Mr Brown’s credibility on the issue he was forced to admit he had exaggerated the scope of the points-based system, which is designed to ensure that only migrants with skills needed by the British economy are allowed to enter from outside the EU.

During the leaders’ debates Mr Brown has repeatedly suggested that low-skilled chefs and care assistants have been excluded from the scheme. In the first debate he said: ‘No care assistants come in from outside the EU.’ In fact, both categories of workers can still come to work in Britain.

Confronted on the issue during an interview with the BBC’s Jeremy Paxman, Mr Brown admitted that the ban had not been implemented, but insisted it would be brought in within the next ‘year or two’.

Meanwhile, a new report from the think tank Migrationwatch found that 2.5million immigrants are set to enter Britain over the next decade, with one million expected in the next five years. The study is based on projections from the Office for National Statistics.

A YouGov poll commissioned by the organisation yesterday also showed that the majority of voters are opposed to Liberal Democrat plans for an amnesty for up to 600,000 immigrants who have been here illegally for more than 10 years.

The poll found 54per cent of people opposed to the idea, with only 30per cent in support. Opposition was even stronger among those considering voting Lib Dem.