Analysis: The bloodless coup came quicker than anyone had expected. But ultimately it was David Cameron and rising Conservative fortunes that did for Sir Menzies Campbell.

Analysis

The bloodless coup came quicker than anyone had expected or imagined. But ultimately it was David Cameron and the rising fortunes of the Conservatives that did for Sir Menzies Campbell.

If it were not for the Tory leader's bravura performance at his party's conference in Blackpool and Shadow Chancellor George Osborne's announcements on tax policy, plus Tory grandee Lord Ashcroft's largesse in ploughing millions of pounds into marginal seats, then Gordon Brown would have called a snap General Election.

All these factors not only led the Prime Minister to rule out a poll on November 1, but to all but rule one out next year, meaning the earliest he would go to the country was May 2009. Yet not even this is guaranteed and events could prove Mr Brown will have to go on to the very end in May 2010.

This stark prospect concentrated LibDem minds, not least, we are told, Sir Menzies's.

A General Election this year or even next spring would have maintained his place at the top as there would realistically not have been enough time for a successor to bed in.

However, the prospect of a poll in 2009 or even 2010 meant that colleagues, ordinary party members and Westminster journalists would be asking at every turn how long the 66-year-old MP for North East Fife would go on. By the spring of 2010, he would just about be entering his 70th year.

While during his reign Sir Menzies had successes, such as winning the Dunfermline and West Fife by-election over Labour, of setting the agenda on polluter-pays taxes and on reorganising the party, many felt the LibDems were haemorrhaging support to the resurgent Conservatives, particularly in the south-west of England.

And while he sought to make a virtue of his age, his previous illness cruelly made the LibDem leader look older than he actually was.

So basically, it was ageism that did for the pensioner from Fife; if he had been 20 years younger would anyone seriously have been questioning his leadership? During the LibDems' autumn conference in Brighton last month talk was dominated by Sir Menzies's longevity as party leader. The best-attended event was a fringe with the two young pretenders, Nick Clegg and Chris Huhne, who will now battle it out for the party crown.

It was at another fringe that the shiny-faced Mr Clegg, a whippersnapper at just 40, famously admitted that, while he would not challenge Sir Menzies, he coveted the leadership and hoped to take the reins sometime in the future.

Elspeth, the Scot's formidable wife, publicly told the young upstart where to get off. Then there was that awful conference image of the leader pointing to an organic toilet.

Speculation was also fuelled by the party's falling fortunes in the opinion polls. The LibDems slumped at one point to 11% compared to 23% at the last General Election.

At the weekend, Simon Hughes, the party president who was an unsuccessful rival to Sir Menzies for the leadership, made an injudicious comment about how his colleague "obviously has to do better" and raise his game.

Sir Menzies tried to brush such talk aside, branding it idle chatter by an "occasional dissident". But over the weekend he sounded out friends. A senior party source explained how "there was a lot of support" but that he began to see the continued speculation "would be very damaging".

Then, yesterday lunchtime, Vince Cable, the loyal deputy leader, let slip how the leadership was "under discussion" while Lord Taverne, a LibDem peer, openly called on his colleagues to pressure the leader to quit soon. He said: "If there's not a change in leadership, the party goes down the drain."

The Westminster grapevine was abuzz. Within two hours of their broadcast comments, Sir Menzies was at the Cowley Street party HQ with a small clique of party grandees, including Lord Rennard.

He apparently told them he had made up his mind that the continuing speculation about his leadership was not going to go away and that it would be corrosive. The senior party source explained: "He told them he had decided to go. He decided to put the party's interests before his own. It was an honourable man doing the honourable thing. Effectively, it was a bloodless coup. It was not et tu Brute'. He fell on his own sword."

Ironically perhaps, it was left to Mr Hughes and Mr Cable at 6.30pm to stand on the steps of party headquarters to announce Sir Menzies's resignation with immediate effect.

Now the battle begins to find the new king. It is Home Affairs spokesman Mr Clegg's to lose. Mr Huhne, who has the environment portfolio and whose profile was raised during the last contest, will be his main and probably only rival.

However, others might not rule themselves out, simply to try to secure themselves good jobs under the new regime.

And, of course, there will be talk of a return of Charles Kennedy, but as one Westminster source noted: "Charlie? He's a busted flush."