Ministers have been forced to concede that more than half of all jobs created since Labour came to power have gone to migrants. They were also forced to clarify again their figures on the number of foreign workers in the country.

On Monday night the Government had said that the number of foreign workers who had taken up jobs in Britain since 1997 was 1.1 million rather than 800,000.

Jacqui Smith, the Home Secretary, insisted nonetheless on BBC News’s Breakfast programme yesterday that the majority of new jobs had been filled “by British workers”.

Later, the Department for Work and Pensions (DWP) issued a clarification saying that 52 per cent of more than 2 million new jobs created since 1997 had in fact gone to migrants.

The confusion over the number of foreign citizens working in Britain then deepened after a letter from the National Statistician emerged which said that 1.5 million people born overseas were employed here.

In the letter, sent in July, Karen Dunnell said: “For the three-month period ending March 2007 there were 1.5 million overseas-born people in employment who had entered the UK in the last 10 years. This figure includes those who were children when they arrived.”

Last night the DWP gave two different explanations for the difference between the 1.1 million and 1.5 million figures.

Initially a spokesman said that the extra 400,000 foreign workers were not filling new jobs but had filled vacancies in established firms.

Two hours later the department issued a new statement which said: “The foreign nationals are not UK citizens, and they make up 1.1 million of the 1.5 million. Therefore the remaining 400,000 are UK citizens.”

Chris Grayling, the Shadow Work and Pensions Secretary, said: “This situation just gets worse. It’s clear we simply can’t trust the figures or statements put out by the Government on migrant workers in the UK”.

In her interview on Breakfast, Ms Smith apologised for the Government’s first figure – 800,000 – being incorrect. She said: “Of course it is bad that these figures are wrong and ministers have apologised for that.”

The row developed as the Government announced that curbs on low-skilled workers from Romania and Bulgaria coming to work in Britain are to be maintained for a further year.

In spite of objections by the Foreign and Commonwealth Office, ministers have decided that the restrictions imposed when both states joined the EU in January must be maintained.

The decision, details of which were disclosed in The Times on Saturday, comes as concern mounts over the scale of immigration. Polling for the two main political parties shows that immigration is one of the top issues worrying the public.

Liam Byrne, the Immigration Minister, said that the restrictions on Bulgarians and Romanians had been reviewed and the controls would remain until “at least the end of 2008”.

He added: “While initial evidence shows that there is a clear positive contribution to the economy from migration, there are some reports of pressures in other areas, including public services. The prudent balance is therefore to maintain restrictions as we monitor the effects of accession migration.”

Under the curbs, low-skilled immigrants from Romania and Bulgaria are restricted to two special programmes for seasonal agricultural labourers and the food processing industry. Only 19,750 are allowed to come to Britain under the schemes. However, the self-employed, highly skilled and those whose skills cannot be found in the existing labour market and have a work permit are allowed into Britain.

In the first six months since the two states joined the EU, 75 people have come to Britain under the Highly Skilled Migrant Programme, 1,095 have received work permits and 7,775 are self-employed.

From next April the Office for National Statistics has said that it will improve its monitoring of immigration at Manchester, Stansted and Luton airports. The International Passenger Survey came under attack last year because its figures concentrated on larger airports.

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