Sir Menzies Campbell hit out last night at plotters within his party for " playing the dangerous game" of undermining his leadership.
The former Liberal Democrat leader appeared to attack supporters of the leadership hopeful Chris Huhne for briefing against him. He told Channel Four News that he believed the environment spokesman was loyal and had integrity. But challenged about Mr Huhne's supporters, he said: "Those who undermine any part of the party, whether it is the leader or the president or the spokesman on social security undermine themselves as much as they undermine the party. It's a dangerous game."
Privately, some MPs blame backers of Mr Huhne for undermining Sir Menzies' leadership.
Sir Menzies told how he felt "irritated and frustrated" at being forced to step down as Liberal Democrat leader, insisting that he found it impossible to shake off the "cloying blanket" of repeated questions about his age and leadership.
In an earlier interview with the BBC, his first since quitting as party leader on Monday, Sir Menzies expressed barely concealed dismay at senior figures in the party who helped to fuel speculation about his position. He said: "Seven days went past in which there were seven consecutive sets of reports about my age and about leadership and it became very clear to me, Gordon Brown having called off the election, that it was going to be very hard to get out from under that."
Sir Menzies insisted the he was not given an ultimatum to quit but said the situation was "continually difficult because the default story in the minds of many people was about my age".
He said that he "had no sense that people were moving against me". But asked about critical comments from senior colleagues he said: "One or two colleagues said, shall we say, different things."
The battle to succeed Sir Menzies will take off today when Mr Huhne becomes the first figure formally to enter the race. Nick Clegg, the party's home affairs spokesman, and bookmakers' favourite for leader, was still consulting colleagues yesterday, although he is thought certain to stand.
Steve Webb, who is writing the party's manifesto, is also likely to stand. Other MPs including Ed Davey, Sir Menzies' chief of staff, and Susan Kramer, the transport spokesman, were also pondering a bid.
Charles Kennedy, the former leader, was said to have been consulting colleagues, although MPs thought it unlikely that he would make the ballot paper. "He is unlikely to do that," said one senior Liberal Democrat MP. "He would be embarrassed, because he would do well to get the required seven nominations."
Sir Menzies used broadcast interviews to blame the media for his treatment and insisted that he was not pushed out of the job.
He said: "I thought long and hard about this and I reached the view without too much difficulty that the interests of the party require that I step down and step down now rather than waiting until Christmas or March.
"My fitness and my stamina is as good as I would want it to be, but I was by no means in doubt that I would get out from under this cloying blanket of speculation about leadership."
Sir Menzies added: "This was my decision. I took this decision. This was my conclusion based on my assessment and based on my understanding of what my responsibility to the party should be. I took the view very firmly that this was not going to be in the interests of the party and that if I were to step down, get out of it now so that a new leader would have the opportunity of bedding himself or herself in."
Senior figures in the party insisted yesterday that they were "moving on" from Monday's events, despite a backlash by some about the manner of his departure.
The Liberal Democrat MP Mike Hancock told the BBC that the treatment of Sir Menzies by some of his colleagues had been "absolutely despicable".
He said: "We just didn't give the poor man a chance." There was, he said,"a right shower who were stirring it behind his back, didn't have the guts to come forward and spell it out to his face or even to the parliamentary party".
That was discounted by many senior figures, although one acknowledged: "Obviously among our colleagues some might have been unhelpful." Another said: "A small group in the Lords have said some unhelpful things."
The contest to succeed Sir Menzies was looking like a battle between the party's traditional left and the modernising "Orange Book" Liberal Democrats from the centre right.
Allies of Mr Huhne said last night one advantage he had was that he had "the bottle" to run for the leadership last time when he came a creditable second to Sir Menzies.
He will appeal to his party as a centre-left candidate leaning towards Gordon Brown, while Nick Clegg, his main rival, will be presented as more right of centre, leaning towards David Cameron, the Conservative Party leader.
Mr Huhne, who held a strategy meeting with his aides at Westminster last night, starts with the advantage of having a team from the 2006 election campaign when he came from a standing start to come second to Sir Menzies. Other campaigners in the party said he also had the advantage of a database containing contact details of his supporters in the country, which could enable him to go into an early lead.
Allies of Mr Clegg say he has the charisma and the correct ideological stance to take the party forward. Mr Clegg can point to success at the party's conference last month with his attacks on the government over civil liberties and immigration. But Mr Huhne can boast that he has helped mark out the Liberal Democrats as the strongest party on the environment.
Ministers believe a shake-up of the Liberal Democrats with a new leader will help Labour at the next election by stopping David Cameron's revived Tories taking more seats in the South. One cabinet minister said: "The Lib Dems were collapsing in the South and the West Country but that could now could be stopped."