Critics have increased the pressure on Gordon Brown after Labour's defeat in the Glasgow East by-election, but colleagues have leapt to his defence. The head of one of the UK's top unions has demanded a leadership contest, while Tory leader David Cameron has called for a general election. But Chancellor Alistair Darling urged Labour to "rediscover the conviction" on which it won three elections. Members are at Warwick University for the party's National Policy Forum. The SNP won Glasgow East - previously considered one of Labour's safest seats - by 365 votes, achieving a 22.54% swing. John Mason, the victorious candidate, said the result was "not just a political earthquake, it is off the Richter scale". It followed Labour's recent loss of the Crewe and Nantwich seat, the London mayoralty and poor results in local elections.