Westminster: The British government has announced "transitional" controls confining lower-skilled workers from Bulgaria and Romania to work in the food processing and agricultural sectors.
British home secretary John Reid said the needs of the UK labour market would be central to decisions on immigration levels.
However, his widely expected announcement also reflected a prevailing political disposition to "draw breath" after an influx of 600,000 workers following the accession of eight former Soviet Bloc countries in the last round of EU enlargement in 2004.
Dr Reid admitted there had been some "transitional impacts" from that expansion in terms of "a small number of schools", local authority problems with overcrowding in private housing and cost pressures on English-language training.
However, Dr Reid faced immediate warnings that his proposed work-permit system would not work and would inflict "lasting damage" on Britain's status as a champion of EU enlargement.
The terms announced yesterday will impose a 20,000 cap on low-skilled workers in food processing and agriculture coming from Bulgaria and Romania, accompanied by the gradual phasing-out of all low-skilled migration schemes for workers from outside the EU. Those who qualify for the highly skilled migrant programme - currently just under 100 a year - will be eligible for entry, and students enrolled at an approved college will be able to work part-time.
Also entitled will be people with specialist skills which cannot be met by resident labour, provided they meet tests on qualifications and earnings. Also allowed will be the self-employed, although there are as yet no forecasts as to how many might fall into that category.
Dr Reid also announced that the so-called "A2" nationals would face on-the-spot fines of up to £1,000 if caught working illegally, with heavy fines also for any employers taking on undocumented workers.
Home Office experts said this raised the prospect of poor workers unable to pay such fines adding further to Britain's prisons crisis, although Romania's acting ambassador to Britain said she expected most of her countrymen looking for work abroad to head for Italy or Spain.
Liberal Democrat spokesman Nick Clegg said it was right to introduce some transitional arrangements. However, he said there were "real concerns" as to how these would work.
"First, the danger of discriminating against all non-EU low-skilled migrants is that they will simply be driven underground into the black economy.
"The second is that there will be little incentive for Bulgarians and Romanians to jump through all Dr Reid's hoops if they know they face only a fixed-penalty notice if they break the rules and will be given unrestricted access in the future."
Former Europe minister Keith Vaz said: "These restrictions will be unworkable, undesirable and unnecessary, and of lasting damage to the reputation of the UK as a champion of the enlargement."