Romanian and Bulgarian workers will not be allowed full access to jobs in the UK, the government has said.
Bulgaria has become part of the EU, along with Romania
Ministers said they supported "managed migration" and that "access for the new member states will be gradual".
Details of the controls for the two new EU countries will be revealed to Parliament by the end of October.
The European Commission has announced that Romania and Bulgaria will be admitted to the EU in January 2007, but under strict conditions.
Formal approval for the two EU newcomers was granted on Tuesday.
Home Secretary John Reid has previously said immigration from the two countries needed to be "carefully managed".
Romania's prime minister, Calin Popescu Tariceanu, told the BBC that concerns about a sudden influx of workers from his country into the UK were misplaced.
"Of course there were Romanians who have left the country in the last 15 years but their destinations were linked to our cultural background," he said.
"That means they prefer to go either in Italy or in Spain because we are a Latin country and they have the capacity to learn the local language.
"I don't foresee a real potential for migration into the UK to work."
Mr Tariceanu said the tone of some of the British press coverage could be insulting and was not justified if it turned into a campaign against his homeland.
"Romania is a country which is highly developed and which will join soon the European Union.
"It is a country which has a very high degree of education, with very skilled people."
Bulgaria's prime minister, Sergei Stanishev, said his country's "integration" would be vital.
"It is important not only that we formally join the EU - although this is a historic event...the final fall of the Berlin Wall for Bulgaria - but it is equally important how Bulgaria's economy will integrate [into the EU]...how we will implement Europe's social model," he said.
Home Secretary John Reid hinted last week that Romanians and Bulgarians would not be given unlimited rights to work in Britain when they join the EU.
The approach contrasts with the government's decision not to impose limits on the number of Polish nationals and others allowed to work in the UK after the previous EU enlargement in May 2004.
While other European governments imposed a range of quotas and other restrictions, UK ministers said the immigrants were needed to fill gaps in the labour market.
The government can only impose restrictions for seven years, after which there will be a free movement of migration and labour.
Latest figures show 427,000 have arrived in Britain from Poland and seven other ex-Soviet bloc states, but the figure may be 600,000 including self-employed workers such as builders.
Original official estimates said there would be no more than 5,000 to 13,000 arrivals a year.
European Commission President Jose Manuel Barroso has previously said the EU cannot cope with any more members after Bulgaria and Romania, until it introduces major decision-making and administrative changes.