Cameron is also lucky in that he has no obvious Tory rival for the top post either, at least not in Parliament. If Boris Johnson were on the backbenches, or could find a way of letting down the voters of London gently, then Cameron would have cause to worry. Boris is a rarity: a popular politician, a phenomenal performer and ideological chameleon to whom the normal rules do not seem to apply. Recently he has even managed to keep a straight face when issuing statements urging his fellow Tories to get behind their leader, surely relishing Cameron's predicament. Boris is determined to become Prime Minister at some point and his supporters are determined to find him a way back into the Commons, although it is extremely difficult to see how it might be done in time for the next election. 

Despite the Prime Minister's advantages, his supporters remain worried and with good cause. The anti-Cameron plotters are a hardcore group of only 25 or so Tory MPs, who spend their time trying to persuade discontented colleagues that something must be done. Although it is unlikely that if they strike they will be capable of removing the Prime Minister, they might do him lasting damage. Tory party rules provide for a vote of confidence in the leader if 46 MPs demand it. In such circumstances, it would rapidly become a test of authority. How many MPs would have to vote against Cameron before he was fatally weakened? The leadership is keen to close this down before it gets to a vote. While those in No 10 were declaring recently that all the leadership speculation was complete rubbish, they were concerned enough to launch a briefing war against the Home Secretary Theresa May and others deemed to be on manoeuvres.

The plotters are only one manifestation of deep unhappiness in the Tory tribe. This has been misunderstood in parts of the London-based commentariat, which thinks that because Cameron is a presentable young man with power, who has read Tony Blair's memoirs, it disturbs the political continuum even to begin contemplating alternatives. As a Tory activist put it to me recently: why wouldn't Cameron's leadership be in trouble? It would be more astonishing if it were not. By the autumn he will have been leader of the Conservative party for eight years. He did not win the election against Labour's Gordon Brown, entered a coalition which his acolytes declared to be superior to a majority Conservative government, and has chosen, recklessly, to offend hitherto core supporters of the Conservatives. There is the tax raid which involves funnelling two million more Britons into paying the higher 40p tax rate, combined with what is perceived as betrayals on pledges to deal meaningfully with inheritance tax and marriage. The introduction of gay marriage instead of tax breaks for married couples by the Prime Minister was just the last straw for some traditional Conservatives. 

Whether they want a change of leader or not MPs still have to return to their constituencies where, unless they are themselves particularly good recruiters, party membership is falling sharply. The number of Tory members across the country is declining so fast that it will soon fall below the 100,000 mark. This has consequences. Having fewer members and activists means it will be tougher to get councillors elected in May's local elections. They are a party's bedrock. Without sufficient councillors it becomes more difficult to put up a good fight at the next election. Take Eastleigh, which only a little more than two decades ago was a safe Conservative seat. When Chris Huhne stood down after being charged with perverting the course of justice, those turning up from Conservative Campaign Headquarters in London and other parts of the country found almost no local structure. They had to scramble together the basics of a campaign with a candidate who seemed ill-prepared for prime-time amid the media-driven madness of a British by-election. In contrast, the Lib Dems were well-dug-in local campaigners with 40 councillors compared to four Conservatives. In other parts of the country thought of as naturally Tory, this debacle is in danger of being repeated. The party machine is being hollowed out.