Just 3,370 asylum seekers were deported in the first three months of this year, compared with 4,085 in the previous three months. The figure is likely to be about 24% behind the Government's own "tipping point" target.

It came as separate figures showed more than one million people have been granted British citizenship since 1997, the year Labour came to power.

Additional data revealed nearly 8,000 Bulgarians and Romanians came to work in Britain in the first three months of this year after their countries joined the EU, plus 2,400 who have joined the seasonal agricultural workers' scheme.

The figures on Romania and Bulgaria did not provide a full picture of the numbers who have moved to the UK because no such records are kept by the Government.

Separate figures showed how many immigrants arrived from the eight former Communist states which joined the EU in the previous wave of expansion in 2004 - known as the "A8" countries. There were 48,820 applicants in the first quarter of this year, down 16,000 on the previous three months.

It brought the total number of A8 immigrants to 630,000 since they joined in May 2004.

However, the figure does not cover self-employed people - a category thought to include a large number working in the construction industry as well as other sectors.

Combining the A8 with Romania and Bulgaria gives a total of 638,000 immigrants. The Home Office did not publish figures on its crucial "tipping point" target, which aims to deport more failed asylum seekers than unfounded cases arriving in the UK.

Prime Minister Tony Blair personally announced the target in 2005 and when John Reid was promoted to Home Secretary a year ago Mr Blair ordered him to make it one of his top priorities. Taking an average of unfounded claims over the previous four quarters as an indicator, it would suggest that the 3,370 deportations was 24% behind Mr Blair's target.