SIR Menzies Campbell last night dramatically quit as leader of the Liberal Democrats, after a weekend of increasing criticism over his leadership and a disastrous slump in the opinion polls.

By Graham Dines

SIR Menzies Campbell last night dramatically quit as leader of the Liberal Democrats, after a weekend of increasing criticism over his leadership and a disastrous slump in the opinion polls.

Just two days after telling Lib Dem members in Mildenhall, Suffolk, that he had the “energy, ideas and determination to leads this party,” he shocked activists and the Westminster establishment by quitting with immediate effect and leaving his deputy Vince Cable in charge of the party.

Although there had been summer long speculation about his future, the threat of a snap election had focused MPs' minds during their party conference last month, dismissing talk of a leadership challenge. But as soon as it was clear that there would be no poll this autumn, and maybe even not next year, the knives were out for Sir Menzies.

Sir Menzies said in a statement: “It has become clear that following the Prime Minister's decision not to hold an election, questions about leadership are getting in the way of further progress by the party.

“Accordingly I now submit my resignation as leader with immediate effect. I do not intend to hold a press conference or to make any further comment.”

The writing was on the wall for Sir Ming earlier yesterday when Mr Cable admitted the leader's future was “under discussion.” Lib Dem peer Lord Taverne warned the party was “going down the drain” under Sir Ming's leadership.

Accompanied by Mr Cable, the party's president Simon Hughes read out a statement on the steps of the party's headquarters saying: “Ming Campbell has this evening submitted his resignation as the leader of the Liberal Democrats with immediate effect.

“For the last two years Ming 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.

“Throughout all his political life Ming has taken all his decisions - and this decision is one of them - in the interests of our party and of liberal democracy throughout Great Britain and every Liberal Democrat and many other people owe him a huge debt of gratitude.”

Both men declined to answer questions and did not respond to questions from journalists which included: “Did you wield the dagger?”

The Lib Dems now face a second leadership contest in less than two years. Sir Ming was elected after Charles Kennedy was forced to resign, admitting he had an alcohol problem.

Favourites to succeed Sir Menzies will include home affairs spokesman Nick Clegg and environment spokesman Chris Huhne.

Paying tribute last night, Euro MP Andrew Duff, the East of England's most senior Liberal Democrat who was one of Sir Ming's closest supporters, said: “He is an honourable man and he has made a dignified exit. He has strong and affectionate support in the party and there will be shock at his going.

“With all the whispers about his leadership, I believe Ming knew that if uncertainty dragged on, the quarrel within the party would have suffered.”

Kathy Pollard, leader of the Lib Dems on Suffolk county council and parliamentary candidate in South Suffolk in both 1997 and 2005, said: “Ming has done a fantastic job in his time as leader, especially in preparing the party for the general election that nearly was. He brought substance to politics at a time when the other two leaders seemed more interested in spin.”

She called on the party to unite behind whoever succeeds him “to the other two parties; especially on climate change, long-term care for older people, council tax reform and the catastrophe in Iraq.”

Mr Cable, who is expected to stand in for Sir Menzies at the weekly Prime Minister's Question Time clash with Mr Brown, said: “Politics is a very brutal business.”