UK immigration from Eastern and Central Europe between 2001 and 2011 was far higher than previously estimated, according to the Office for National Statistics.
It has admitted to getting its figures wrong by around 346,000 because its surveys did not concentrate on a number of routes connecting the UK and the Continent.
While the ONS mainly monitored figures at Heathrow, Gatwick and Manchester airports, large numbers of migrants were arriving via Luton, Stansted and regional aiports. Overall, the number of routes between the UK and the EU jumped from 30 to 190 between 2001 and 2007, The Guardian reported.
The ONS International Passenger Survey (IPS) also did not accurately count the number of children arriving in the UK with their parents.
An ONS spokesman said: "ONS recognised with the publication of 2011 census data that the IPS had underestimated migration between 2001-11. We published revised overall net migration figures in 2013, and the [new] data published updates the historical series to make it consistent with those.”
Prime Minister David Cameron is aiming to reduce net migration to the UK to below 100,000. The Government has already set limits on the benefits that out of work EU migrants can claim and is now aiming to expand the system to reduce child welfare benefits for the children of unemployed migrants.