Gordon Brown has announced he will step down as Labour leader by September - as his party opens formal talks with the Lib Dems about forming a government.

在英国工党与自由民主党关于组建政府的正式会谈上，戈登·布朗宣布退出工党的领导地位。

The PM's continued presence in Downing Street was seen as harming Labour's chances of reaching a deal.

Labour and the Tories are both trying to woo（追求，恳求） the Lib Dems with promises on electoral reform as the battle to run the country reaches its critical phase.

No party won a Commons overall majority at the Thursday's general election.

The Tories, who won the most seats and votes, reacted to Mr Brown's announcement that he was standing¹ down as Labour leader by making a "final offer" to the Lib Dems of a referendum（公民投票） on changing the voting method to the Alternative Vote (AV备择性选举) system.

Labour are offering to put the AV system into law and then hold a referendum asking voters to approve it.

'Progressive majority'

It is now understood the Lib Dems are seeking a full coalition²（联合，结合） with either Labour or the Conservatives.

A senior Lib Dem source indicated that he expected a resolution to the process of shaping the new government to be reached within the next 24 hours, saying that tomorrow was "crunch³ time".

A meeting of the party's MPs continued beyond midnight and ended with no firm decisions taken, the BBC understands.

BBC political editor Nick Robinson said Mr Brown's resignation was an audacious（无畏的，鲁莽的） bid by Mr Brown to keep Labour in power - and himself in power for a limited period - and that Tory MPs would be furious（狂怒的，激烈的） .

In his statement, Mr Brown said Britain had a "parliamentary and not presidential system" and said there was a "progressive majority" of voters.

He said if the national interest could be best served by a coalition between the Lib Dems and Labour he would "discharge that duty to form that government".

But he added that no party had won an overall majority in the UK general election and, as Labour leader, he had to accept that as a judgement on him.

Leadership process

"I therefore intend to ask the Labour Party to set in train the processes needed for its own leadership election.

"I would hope that it would be completed in time for the new leader to be in post by the time of the Labour Party conference.

"I will play no part in that contest, I will back no individual candidate."

He has urged potential candidates, such as Foreign Secretary David Miliband and Schools Secretary Ed Balls, not to launch their campaigns yet. Harriet Harman has ruled herself out of the race, saying she wants to continue as deputy leader.

Lib Dem leader Nick Clegg had requested formal negotiations⁵ with Labour and it was "sensible and in the national interest" to respond positively⁶ to the request, Mr Brown said.

It emerged earlier that the Lib Dem negotiating team, who have held days of talks with the Conservatives, had also met senior Labour figures in private.

But it was understood that one of the stumbling blocks（绊脚石） to any Labour-Lib Dem deal was Mr Brown himself.

Mr Clegg said he was "very grateful to David Cameron and his negotiation⁴ team" and they had had "very constructive⁷ talks" and made a "great deal of progress".