Migrants contributed about £6 billion to economic growth last year, according to new Government figures.
The Home Office's analysis of the economic impact of foreign workers came as immigration minister Liam Byrne admitted it had been a "mistake" to remove exit checks at Britain's borders.
Treasury estimates in the figures showed migration added 0.5% a year to the working age population between 2001 and 2006.
"On this basis, migration contributed around £6 billion to output growth in 2006," the document said.
It also found migrants earn more than UK workers on average - £424 a week compared with £395.
A Home Office spokeswoman said: "There is a range of evidence that suggests that, overall, the economic impact of migration is beneficial for the UK.
"In recent years migrants have made a more positive contribution to the public finances than native workers."
In a speech delivered at his former school in Harlow, Essex, Mr Byrne outlined forthcoming immigration changes and said: "We'll start to count people in and out of the country, because removing exit checks was a mistake."
Contracts connected with the new e-Borders system to introduce electronic checks will be signed within the next 30 days, he added.
Exit checks were dropped in several waves under the previous Conservative government and under Labour from 1997. Not having access to data on how many people leave the country has made it impossible to estimate how many illegal immigrants are now in the country.
