LONDON, Oct 15 (Reuters) Menzies Campbell, leader of the centrist Liberal Democrats who consistently opposed the Iraq war, resigned today as head of Britain's third biggest party after his and his party's support slumped in opinion polls.
Party President Simon Hughes announced the 66-year-old former Olympic sprinter's departure in a brief and unexpected statement.
Campbell had been criticised for his lacklustre performance in parliament, and party colleagues feared he would have been an ineffective leader if Prime Minister Gordon Brown had called a snap election.
''Sir Menzies Campbell has submitted his resignation as the leader of the Liberal Democrats with immediate effect,'' Hughes said in a brief statement to reporters.
''For the last two years Menzies has given huge purpose and stability to our party. He has led the professionalisation of the party and he has led the very successful preparations for the general election, whenever it comes,'' Hughes said.
The party's support in opinion polls has halved since the 2005 general election to just 11 per cent, trailing behind the ruling Labour Party and the main opposition Conservatives.
Earlier today the Liberal Democrats' deputy leader, Vince Cable, admitted Campbell's future was ''under discussion'', and his resignation followed a tumultuous two weeks in British politics.
After just 100 days in office, Prime Minister Gordon Brown was pilloried for making a U-turn when he ruled out an early election, and was accused by the Conservatives of stealing their policies.
Brown, who took over from Tony Blair in June after 10 years as his finance minister, had been widely expected to call an election 2-1/2 years earlier than necessary.
His opinion poll lead over the Conservatives suddenly evaporated and he said there would be no early election -- saying the polls had not been responsible for the decision.
Campbell, widely praised for his foreign policy expertise and knowledge, became Liberal Democrat leader in March 2006.
He was considered a ''safe pair of hands'' who could stabilise the party after his predecessor Charles Kennedy stepped down, admitting he had an alcohol problem.
Under Kennedy, the party achieved its best ever result in the May 2005 general election, winning 22 per cent of the vote -- but less than 10 per cent of the seats in parliament under Britain's first-past-the-post electoral system.
REUTERS CS BST0048