Mr Lammy, a 27-year-old black barrister who grew up in his new constituency, succeeds veteran left-wing MP Bernie Grant, whose death caused the contest.

The heartlands of Tottenham are safe in the hands of New Labour

David Lammy MP

He took 53% of the vote, suffering a 12% swing away from Labour to the Lib Dems who snatched second position from the Tories.

Only about one in four voters turned out for the election compared to 57% in 1997.

Lib Dem candidate Duncan Hames said: "We've nearly doubled our share of the vote and shown Liberal Democrats are the clear alternative to Labour in the heartland cities of this country.

"William Hague's Conservative Party must be feeling quite horrified with today's result."

Conservative chairman Michael Ancram said his party's candidate Jane Ellison had suffered from Tory supporters staying at home.

Ambition

Mr Lammy, from a low-income single parent family, said he knew what it was like to grow up disadvantaged in Tottenham but pledged to work towards improving employment, schools and housing in the area.

He said: "It is about ambition for our people, for our schools.

Bernie Grant had held the seat since 1987

"The heartlands of Tottenham are safe in the hands of New Labour."

He also paid tribute to Guyana-born Mr Grant who had held the seat since 1987 before he died in April this year after a heart attack aged 56.

Mr Grant first won the seat by 4,000 votes, but by 1997 he had increased his majority to 20,200, making the seat one of Labour's safest.

Mr Lammy, undaunted by his predecessor, becomes the baby of the Commons - being just three weeks younger than Christopher Lesley, his party colleague from Shipley, Yorkshire.

He is also a member of the new Greater London Assembly but has said he would resign his seat there if elected to the House of Commons.

Opposition attacks

Mr Lammy had been criticised during the campaign for being too close to the Labour leadership and opposition parties used the result to launch fresh attacks.

Lib Dem leader Charles Kennedy said: "The Liberal Democrats are the only party able to claim success from the Tottenham result.

"It shows that, while there is no enthusiasm for Labour - even in its inner-city heartlands, there is no sign of a Tory revival either."

Mr Ancram said many Tory supporters took the result for granted and stayed at home.

He said: "Given the left-wing nature of the constituency and the low turn-out, the Liberal Democrats have performed well.

"The Liberal Democrats used their election literature to engage in personal attacks on our candidate - typical Liberal Democrat campaigning in action."

Tottenham by-election results: