European workers now make up 6.8% of Britain's workforce of 31.5 million, according to recent figures from the Office for National Statistics (ONS).
Supporters of the Vote Leave campaign said the latest numbers were evidence of "uncontrolled migration".
But the prime minister's office said the broader point was that the UK economy was growing.
The number of EU workers in the UK workforce has risen by 224,000 in the past year, an increase of 11.7%.
During the same period the overall UK workforce has increased by 1.3%.
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Vote Leave's Iain Duncan Smith said poorly-paid or unemployed British workers were being "forced to compete with millions of people from abroad for jobs, and they suffer downward pressure on their wages".
UKIP said the latest employment statistics "showed why we need Brexit to put British workers first".
UKIP employment spokeswoman Jane Collins MEP said the free movement of people and the 2.15 million workers from the EU now in the UK was "a huge boon to multinational companies who can exploit the oversupply of labour to keep their wages low".
It was "not so good for the parts of Britain with serious unemployment problems", she added.
But a spokesperson for the prime minister said: "It is good that we've got a growing economy and we're seeing record numbers of British nationals in employment."
The Department of Work & Pensions (DWP) said the employment rate for Britons was the highest since record-keeping began, and that since 2010 the number of British people in work had increased by 1.5 million.
The government has taken action "to protect the benefits system and ensure migrants come to this country for the right reasons," said a DWP spokesman.
Official figures released on Wednesday showed the jobless rate remained at 5.1%, in the first quarter of 2016.
The Office for National Statistics added there were 31.58 million people in work, up 44,000 from the previous quarter.
That took the employment rate to a record high of 74.2% in the three months to March.
Prof John Van Reenen, director at the Centre for Economic Performance at the London School of Economics, says that while it may be tempting to assume that Europeans are taking jobs that might otherwise go to British workers, the overall picture is far more complex.
"In certain occupations, there is a negative impact" from the arrival of European workers, Mr Van Reenen acknowledged. But when economists examined the effects of European immigration to specific regions of the UK, they found a negligible impact on British unemployment rates in those regions.
"It doesn't seem to be obvious from the data that this is happening," he said.
But Conservative MP Dr Liam Fox, who is campaigning to leave the EU, says that European migrants are putting Britain's public services under strain.
"People can feel that in their daily lives by the lack of school places, the difficulty seeing a GP and the competition for housing," he told the BBC's Norman Smith.
"And of course those who fund the Remain campaign... Goldman Sachs, the big banks, the big corporates, the oil companies, they don't really care because they don't use those particular services," he added.
Downing Street has sought to play down figures showing that EU workers in the UK have risen to a record 2.1 million.