Gerry Sutcliffe, the 41-year-old leader of Bradford city council, polled more than 54 per cent of the vote as Conservative support collapsed and Liberal Democrats failed to fill the void.
Mr Sutcliffe stormed home with 17,014 votes against 5,475 for the Conservative candidate, Ronnie Farley. The Liberal Democrat candidate, Helen Wright, took second place with 7,350 votes.
Mr Sutcliffe succeeds Bob Cryer, whose death in a car crash caused the by-election. Mr Cryer's best result, secured at the 1992 general election, gave him 47 per cent of the vote with the Conservatives second on 38 per cent. Turnout at the by-election yesterday was 45 per cent, down by 30 percentage points compared with the general election.
Mr Sutliffe said the most startling characteristic of the poll was the collapse of Conservatism. 'The Tories have stayed at home, no longer prepared to vote for their own party,' he said.
'Among Labour voters the penny has dropped. They see Labour as a party determined now to get power, making a Labour government the priority on the party's agenda.
'John Smith spoke in Glasgow of his determination to return this country to decent government. We will dedicate this victory to him.'
Ms Wright said that she had been confident that the Liberal Democrats would push the Conservatives into third place. The bottom had dropped out of the Tory vote in the seat and left the Liberal Democrats as the main challengers to Labour, she added.