The British Home Secretary John Reid said that the UK would take as many skilled workers as it needed but low-skilled workers would be limited to just 20,000.
He said that those in low-skilled or unskilled jobs would have "no automatic right" to come and work in Britain.
"The important thing is to try and achieve that balance between the needs of the economy and the protection of our society," Mr Reid said.
Bulgarian foreign ministry spokesman Dimitar Tsanchev said the nation was "disappointed", adding the move put Bulgaria "in a situation of inequality" against nations which joined the EU in 2004.
And the acting Romanian ambassador to Britain, Raduta Matache, told BBC radio she believed that fears of her compatriots flooding into Britain were "totally unfounded", adding most would probably go to Italy or Spain.
EU 'regret'
Most EU nations remained undecided on whether to grant unfettered access to workers from Bulgaria and Romania next year.
When a wave of ten nations including Poland joined the EU in 2004, Britain was one of only three countries to allow unrestricted access, a policy which Reid defended as "a success".
Prime Minister Tony Blair's administration predicted that up to 13,000 people from eastern Europe would come to Britain, but so far up to 600,000 have arrived.
EU employment and social affairs spokeswoman Katharina Von Schurbein expressed "regret" that countries which had previously opened their borders would not do so for the two new members, but did not specifically mention Britain.
Restrictions
In a written statement, Home Office junior minister Liam Byrne said low-skilled workers would be restricted to existing quota levels to fill vacancies in agriculture and food-processing.
Skilled workers would be able to work in Britain if, as is currently the case, they get a work permit to take up a job where no suitable UK applicant can be found, or qualify under a programme for highly skilled workers.
There will be an annual review of the restrictions and a new committee will advise on quota management.
Britain's Press Association (PA) news agency said the total minimum number of Bulgarians and Romanians likely to come to Britain under the plans was around 23,000.