Defeat left Brown facing a bleak weekend as the party's main policy-making forum met to try to work out how to win back voters disillusioned by a string of political gaffes, rising inflation and a slowing economy.

Adding to the gloom, data published on Friday showed second quarter growth slowed to its weakest rate in three years as housebuilding slumped, dragging the annual growth rate down to 1.6 percent from 2.3 percent in the first quarter.

The pro-independence Scottish National Party (SNP) snatched a slim 365-vote majority in the Glasgow East constituency with a 22.5 percent swing that overturned the 13,500 majority enjoyed by Labour at the 2005 election.

If that swing against Labour was repeated in a general election even Brown could lose his seat.

In more bad news for Brown, a poll for The Independent on Saturday showed the Conservatives opening a 22-point lead over Labour.

That would give the Conservatives a landslide victory at the next general election, which Brown must call by May 2010.

The Glasgow result, the latest in a series of local and parliamentary election defeats for Labour, raised questions about whether Brown will face a challenge to his 13-month-old leadership of the party.

"We need a new start. We need to look fundamentally at the policy direction for the next general election and I think we need to have that debate around a leadership election, with or without Gordon," Labour MP Graham Stringer told the BBC.

The Guardian said in its Saturday edition that discussions were under way at cabinet level on whether to seek Brown's "orderly resignation" while The Independent said Labour legislators were urging senior ministers to tell Brown to quit.

Labour's defeat prompted Conservatives to demand a general election after the summer and sparked an inquest into Labour's direction among party members and trade union backers.

WANING POPULARITY

Union leader Paul Kenny said the debate over Brown's leadership had to be settled. "Either there is confidence in Gordon Brown as leader ... or this will rumble on ... and we will remain a divided organisation," he said.

Brown's popularity has slumped in the 13 months since he replaced Tony Blair, who had led Labour to three successive election victories since 1997.

Brown pledged to battle on. "I think my task is to get on with the job of taking us through these difficult economic times," he said.

Wyn Grant, politics professor at Warwick University, told Reuters the Glasgow result was a "huge protest vote", but was sceptical it would lead to a serious attempt to oust Brown.

Brown promised steps to help families with housing and fuel bills. But power utility EdF Energy said it was raising electricity prices by 17 percent and gas by 22 percent, squeezing hard-pressed consumers further.

The Glasgow East election was called after the Labour incumbent stepped down due to ill health. The constituency has areas scarred by unemployment and alcohol and drug addiction.

The sharp swing from Labour to the SNP is not just a political but also a personal blow to Brown, a Scot, although Labour still has a 62-seat majority in parliament.

(Additional reporting by Matt Falloon in London; writing by Adrian Croft and Jeremy Lovell; editing by Sami Aboudi)