Ed Miliband resigned as leader of the U.K.’s opposition Labour Party after it looked set to record its worst defeat in almost three decades, including losing all but one lawmaker in Scotland.

Miliband, whom pollsters had until Thursday portrayed as neck-and-neck with Conservative Prime Minister David Cameron, made the announcement in a speech in central London on Friday.

"I take absolute and total responsibility for the result and our defeat at this election," he said. "Now it’s time for someone else to take forward the leadership of the Labour Party."

Labour was on course for its worst result since Neil Kinnock’s defeat in 1987.

Miliband’s resignation as leader was the third of three by party leaders on Friday, with Liberal Democrat leader Nick Clegg and U.K. Independence Party Nigel Farage announcing they were stepping down.

The Scottish National Party took 40 of Labour's seats in an election sweep that saw them win 56 of Scotland's 59 districts.

Miliband’s position, weakened by the Scottish losses, became untenable after finance spokesman Ed Balls lost his seat in Parliament to the Conservatives. Deputy leader Harriet Harman will take over leadership of the party until a new leader is elected, Miliband said.

"The party needs to have an open an honest debate about the right way forward without constraint," Miliband said. "We’ve come back before and this party will come back again."

The bookmakers Ladbrokes made health spokesman Andy Burnham and business spokesman Chuka Umunna favorites to succeed Miliband.