London - Britain's ruling Labour Party suffered a stinging defeat in a by-election in the Scottish city of Glasgow which analysts believe is a further severe political setback for Prime Minister Gordon Brown.

The Scottish National Party (SNP) unseated Labour in the constituency of Glasgow East, which had been a Labour stronghold for decades.

The SNP snatched power from Labour at regional level in Scotland last year, after 40 years of Labour domination.

The swing from Labour to the SNP in Glasgow East, a deprived area of Scotland's second city, was 22 per cent. Turnout was 42 per cent.

The setback comes after two recent losses for Labour in by-elections in Britain, which analysts have said are proof of the unpopularity of the Brown government.

But the Labour government says the trend is due to factors like the deteriorating world economy and "mid-term blues."

The SNP described the result in Glasgow East as a "political earthquake."

David Cameron, the leader of the opposition Conservative Party at national level, Friday called on Brown to call an early general election as it was now clear that the Labour government was "extremely unpopular." (dpa)