The former Cabinet minister confirmed for the first time that New Labour not only welcomed but actively encouraged that mass influx of migrants.

He conceded that this now poses a major difficulty for the party’s traditional supporters, according to the Daily Mail.

Earlier this year Ed Miliband admitted that the last Labour government was not “sufficiently alive to people’s concerns” over immigration and his party got “the numbers wrong”.

But the party leader stopped short of admitting that immigration was too high.

Between 1997 and 2010, more than 2.2 million immigrants came to the country – more than twice the population of Birmingham – with the annual net figure quadrupling during their time in office.  

 Lord Mandelson admitted: “In 2004 when as a Labour government, we were not only welcoming people to come into this country to work, we were sending out search parties for people and encouraging them, in some cases, to take up work in this country.”

In the past senior figures have denied that they engineered immigration, and three years ago refuted suggestions from adviser Andrew Neather that they encouraged the process to make the UK “truly multicultural” as a snub to the right.