Britain's ruling Labour Party lost one of its safest parliamentary seats, results showed on Friday, deepening doubts within the party about Prime Minister Gordon Brown's ability to win the next election.
The pro-independence Scottish National Party snatched a slim 365-vote majority in the Glasgow East constituency, overturning the huge 13,500 majority enjoyed by Labour at the 2005 election.
The defeat leaves Mr Brown facing a bleak political weekend as the party's main policy-making forum meets at Warwick University to try to figure out how to win back disillusioned voters.
The election was called after the Labour incumbent stepped down due to ill-health. The 22% swing from Labour to the SNP - many traditional Labour supporters switched sides - is not just a political but also a personal blow to Mr Brown, a Scot. But the result barely dents Labour's 62-seat majority in Westminster.
However, following a series of recent Labour election defeats, the result will strengthen expectations that the party's 11 years in power may be nearing an end and that it could lose the next general election, due by early 2010.
"This SNP victory is not just a political earthquake - it is off the Richter scale," jubilant SNP candidate John Mason said. The seat was considered Labour's third safest in Scotland.
PM's popularity slides
The defeat adds to the deepening sense of crisis enveloping Mr Brown, whose popularity has slumped since he took over as prime minister from Tony Blair 13 months ago.
Mr Brown and Labour have been hurt by the credit crisis, which has hit economic growth and sent house prices sliding, as well as by rising food and energy bills.
He has also made blunders, pulling back from calling a snap general election last year and pushing through tax reforms that hit low earners before he was forced into concessions.
At the Warwick University meeting this weekend, Mr Brown will face not just dismayed party loyalists but disgruntled leaders of the trades unions on which Labour relies for funding. Many of them are in open revolt saying the party has forgotten the poor.
Unions have brought a long list of demands to the table - including more powers to strike and free school dinners, but Mr Brown is expected to give little ground.
The broad strands of the Labour movement - from socialists to modernisers - are increasingly at odds about where to go next and how to win a fourth term.
The anxiety is increased by the fact that Labour lags the opposition Conservatives by up to 20 points in national opinion polls, enough to give the Tories an easy victory at the next general election.