More than 120 Romanian and Bulgarian immigrants are arriving in Britain every day, the Home Office revealed.
The figures - the first since the two countries joined the EU in January - show 10,535 have registered to work in Britain in the last five months.
Some 40,000 more are predicted to arrive by the end of the year. And many will presumably be seeking employment in a Big Top.
For rather than the plumbers and builders many expected, the top profession listed by Romanians is "circus artiste". Most Bulgarians claim to have worked as chefs or caers while musician, researcher and hotel worker also make the cut.
At the same time, the flood of migrants from other eastern European countries shows no sign of abating. More than 49,000 entered the UK in 2006, putting the total number registered with the Home Office at 630,000 - a far cry from the Government's initial estimate of 13,000.
But officials admit this could be the tip of the iceberg, as the figures do not include the self-employed, spouses, children or those who do not bother to register.
Conservative shadow immigration minister Damian Green said: "This blows out of the water the Government's proclamation that just 13,000 workers a year would arrive from the eight former eastern bloc countries."
Sir Andrew Green, chairman of Migration Watch UK, said: "The latest figures confirm that massive levels of immigration from Eastern Europe continue unabated.
"The extra 10,000 from Romania and Bulgaria that the Government knows about is a further addition to the total.
Scroll down for more
"This makes it even more essential to reduce immigration from elsewhere."
Critics are now warning that key public services, including schools and hospitals, could be put under increasing pressure.
Business leaders say they are concerned that up to half a million British youngsters may find
themselves out of work.
To tackle the problem, ministers have promised to limit the number of work permits handed out to Eastern Europeans to 20,000.
But critics have pointed out that the Government can do little to stop immigrants travelling to Britain or claiming to be selfemployed.
David Frost, director general of the British Chambers of Commerce, said: "The Government must understand that migration is not a long-term solution to the tragic skills shortages that many young people have.
"Over 500,000 18 to 24 year olds are presently out of work. Yet no one seems to notice because many of the jobs have been filled by willing migrant workers.
"This is unsustainable and we are in danger of creating a two tier society, with many going straight from school to a life on welfare."
There has also been a big surge in the number of migrants from Eastern Europe claiming benefits. Some 91,994 cases have been
reported in six months - up 31 per cent on last year - at a cost of £100million to the taxpayer.
It is likely to embarrass the Government, which had claimed migrants were likely to be young men with no interest in receiving state handouts.
Since January, there have been 744 successful applications for Income Support (worth £57.45 a week), 1,858 for Job Seeker's Allowance (also worth £57.45 a week) and 46 for State Pension Credit (which gives a guaranteed income of £114.05 a week).
Some 57,657 are raking in child benefit (£17.45 for the first child and £11.70 for each further youngster), 30,749 are receiving Tax Credits (worth up to £5,200 a year) and 235 families have been given local authority housing.
Immigration Minister Liam Byrne said: "While it remains too soon to evaluate the full impact of the accession of Bulgaria and Romania to the EU, the early indications are that our policy of restricting access to the UK's labour market is helping to ensure that only those who have something to offer the UK are allowed to work here."