The number of Romanian and Bulgarian migrants working in the UK has increased by more than a quarter in three months, according to newly released official figures.
The Office for National Statistics said that between April and June this year141,000 were in employment, which was an increase of almost 26 per cent on the 112,000 working in the previous three months.
This also demonstrates a 35 per cent increase from the same period 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"
Government ministers have declined thus far to estimate the number of people it expects to arrive in the UK when the labour market becomes fully accessible to the two countries.
Officials from Romania and Bulgaria have repeatedly attempted to quash fears that their could be a wave of immigration from their countries.
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.
Additional reporting by PA