The number of Romanians and Bulgarians working in the UK has risen by more than a quarter in three months, official figures revealed.
The Office for National Statistics said that 141,000 were employed during the period from April to June, an increase of almost 26% on the 112,000 in the previous three months. This represents a rise of 35% from the same time last year.
Laws restricting the types of jobs migrants from the two countries can do will be relaxed from the start of next year in light of EU rules, prompting fears of a sharp rise in numbers coming to Britain.
Sir Andrew Green, chairman of Migration Watch UK, said: "This increase of just over a third in Romanian and Bulgarian workers in the UK over the past year is a sharp increase on the previous trend.
"It suggests that still larger numbers will arrive next year when our labour market is fully open to them. This is consistent with our central estimate that net migration from Romania and Bulgaria will run at about 50,000 a year for the next five years"
The Government has so far refused to put a figure on the number of people it expects to come to the UK when the labour market becomes fully open to the two countries.
Officials from Romania and Bulgaria have repeatedly attempted to allay fears over a wave of immigration from their countries.
Earlier this year Bulgarian ambassador Konstantin Dimitrov estimated between 8,000 and 10,000 would enter Britain during 2014, while ambassador Ion Jinga predicted 20,000 might arrive from Romania.
A new Immigration Bill announced in the Queen's Speech will make it easier to remove people from the UK by limiting rights to appeal and tightening the use of human rights law, as well as access to health care.