Tougher penalties, and a cap on the number of low-skilled workers, formed the key part of a package of measures that, the Home Secretary admitted, would be difficult to police.

The number of low-skilled workers from the two states who will be allowed to work in Britain will be 19,750, and they will only be employed in the food-processing and agricultural sectors. However, an unpredictable number will be free to travel to work here if they are self-employed.

Other immigrants to be admitted, after Bulgaria and Romania join the EU in January, will be those who qualify for the highly skilled migrant programme. This is currently just under 100 a year from both states.

Students who are enrolled at a government-approved college or university will be able to come to Britain and work part-time. Last year they numbered 1,213.

Immigrants with skills that cannot be matched by resident labour, and who also meet tests on qualification and earnings, will also be admitted with a work permit. Last year this group numbered 1,740.

These groups total 22,800 — excluding the self-employed.

Previous estimates suggested that self-employed immigrants in the last EU expansion, in May 2004, made up an additional third of the overall total.

If this trend is repeated when Bulgaria and Romania join, it suggests that more than 30,400 migrants from the new EU states may seek work.

Even with yesterday’s list of measures, the Government cannot prevent Romanians and Bulgarians travelling to Britain. There are also fears that the work restrictions will simply drive migrants into the black economy.

The Home Secretary told MPs, in a written statement, that low-skilled Romanians and Bulgarians would only be able to work in special employment schemes for seasonal agricultural work and food processing. He promised employers that, if there were job shortages in other areas, he would consider setting up other, sector-based schemes. But, he said, there would have to be a genuine labour shortage.

An immigration advisory committee, which is yet to be set up, will advise ministers on how quotas for low-skilled immigration are managed.

Liam Byrne, the Immigration Minister, said that a bigger Europe was good for Britain and good for British jobs. But, he said, the country needed to understand the transitional impact from the last round of EU expansion in May 2004.

He said: “This is why we have decided on a gradualist approach this time, taking into account the needs of our labour market, the impact of EU expansion and the positions adopted by other member states.” He admitted that the large number of immigrants who have arrived from the eight Eastern European states that joined the EU in 2004 had caused strain on public services and schools.

The Department for Education and Skills will provide £400,000 to fund a programme to support schools that have limited experience of teaching English to new migrant pupils.

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