The link between immigration from Eastern Europe and youth unemployment has been questioned in a report by campaigners.
The number of migrants working in the UK who were born in Eastern Europe rose by 600,000 since the so-called A8 countries joined the EU in May 2004, while youth unemployment rose by almost 450,000 in the same period, Migration Watch UK said.
Sir Andrew Green, the campaign group's chairman, said it would be "a very remarkable coincidence if there was no link at all between them".
Migrants from the A8 countries - Poland, the Czech Republic, Hungary, Slovakia, Slovenia, Estonia, Latvia and Lithuania - "have tended to be disproportionately young, well-educated, prepared to work for low wages and imbued with a strong work ethic", he said.
Youth unemployment in the UK increased from 575,000 in the first quarter of 2004 to 1,016,000 in the third quarter of 2011, figures from the Office for National Statistics (ONS) show.
Over the same period, the number of workers from the A8 grew by 600,000.
Sir Andrew conceded that measuring any impact of immigration on youth unemployment was "not an exact science".
He said: "Correlation is not, of course, proof of causation but, given the positive employability characteristics and relative youth of migrants from these countries, it is implausible and counter-intuitive to conclude - as the previous Government and some economists have done - that A8 migration has had virtually no impact on UK youth unemployment in this period.
"We hear a great deal from employers about the value of immigrant labour, especially from Eastern Europe, but there are also costs some of which have undoubtedly fallen on young British born workers."
A Home Office spokesman said: "This Government is working to reduce net migration from the hundreds of thousands to the tens of thousands, levels we last saw in the 1990s."