The end is nigh for Iain Duncan Smith, and it comes not a moment too soon

Admittedly, there are some cats willing the crippled mouse to stay alive; 400, on the Labour and Liberal benches in the Commons

Years ago, I sometimes stayed in a ramshackle old house, in which the most innocent of corridor-creeping was hazardous. This was because of a cat. A champion mouser, the moggy was also a sadistic one. It would frequently torture its captives 80 per cent to death and then leave them in a pathetic quiver, hoping that they would revive sufficiently to provide more sport later. Sometimes, the mice would manage to crawl under the nearest piece of furniture, to die malodorously. More often they would just tremble where they lay. This meant that before moving around in the middle of the night, it was wise to put on lights and glasses. The victims did require euthanasia, but preferably not with one's bare feet.

I thought back to those mice last week, when considering the latest stage in IDS's descent into haplessness. If ever a politician needed to be put out of his misery, and as swiftly as possible, it is he. After the Tory conference and that dreadful speech, the humane killers were preparing themselves. At least 25 MPs had their pens poised, ready to write to the chairman of the 1922 Committee, Sir Michael Spicer, requesting a vote of confidence which would bring down the curtain on the farce. Now, the execution has had to be postponed, because of Sir Philip Mawer's report into Michael Crick's allegations about Betsy Duncan Smith's salary.

This is an irrelevance. The real question should not be the payments to Mrs Duncan Smith, who is value for money, but those to her husband, who is not. Yet the Conservative Party will have to remain adrift until Sir Philip finishes his work, and it is drifting ever closer to an election.

The Crick/Mawer process has, however, disclosed further evidence of the Tory leader's incapacity. Senior officials at Central Office - and parliamentary candidates with seats to win - would never have gone public with their anxieties unless they had been serving in a most unhappy ship. That is IDS's fault. He has not only forced the party to pay out hundreds of thousands in redundancy cheques because of bad appointments and an inability to use good people properly. He is also casually rude to junior employees who cannot answer back, but who can move to better-paid jobs.

Around the time when I was trying to avoid standing on mice, I would also try to avoid being mauled by a lioness, for I was occasionally required to brief Margaret Thatcher. That was a bracing experience. I doubt if anyone ever went to a meeting in the Thatchery, as her office was nicknamed, without some tightening of the stomach muscles. Nor did she regard any speech-writing session as satisfactorily concluded until she had tossed and gored several persons.

But her aggression, which could be formidable, was intellectual in origin. She was testing ideas and material; she was also psyching herself up in order to perform at her best. However hard people were driven, however late they were kept up, they knew that in the end they might have made a little contribution to a big performance.

That made everything seem worthwhile, which is hardly the case at the moment. Moreover, Mrs Thatcher was courtesy itself in small matters. IDS has been known to bark at researchers to fetch him a glass of water. It was inconceivable that Margaret Thatcher would ever have behaved like that. She would have been on her own feet, asking if anyone else also wanted something. She knew instinctively what IDS should have learnt in the Army; that an officer should look after the men under his command.

Now, the command has almost disintegrated. If IDS combined the finest qualities of Washington, Churchill and Thatcher, he would find it difficult to recover. As he is merely himself, it is unthinkable. In Macbeth's words: "The time has been, that when the brains were out, the man would die, and then an end.'' Until IDS's end, he can only shuffle on like some apparition at a Haitian carnival.

Admittedly, there are some cats still trying to will the crippled mouse to stay alive; more than 400 of them, on the Labour and Liberal benches in the House of Commons. Over the next few weeks, Tony Blair and his MPs will mask their batteries at Prime Minister's Questions. They will do nothing to finish off Mr Duncan Smith, if the Tory party fails to do so.

But the Tories will not fail to ditch Mr Duncan Smith. Patrick Cormack's intervention over the weekend was a testament to the size of the potential rebellion Nor would a leadership challenge be a threat to party unity. Last week, without pronouncing on the leadership, John Major warned fellow Tories about the dangers of disunion. As one would expect from a former leader who had to spend six and a half years in a futile struggle against his party's anarchic, self-destructive tendencies, Mr Major spoke with feeling. Even so, he is overstating the Tories' current problems. In his day, the party would not be led. A significant number of Mr Major's own backbenchers were determined to give him the doubt of any benefit; to dig away at any policy disagreement until it became an ideological chasm. Things have now changed, partly because heavy defeats have hammered lessons into the thickest of skulls.

Successful policy work, a gentler way of creating harmony, has also played a healing role. The policies announced in Blackpool were generally thoughtful, and commanded general assent. The heat has gone out of the European argument; fewer than six Tory MPs oppose a referendum on Giscard's constitution for the European Union. Indeed, the Tory parliamentary party is more united on the main issues of the day than it has been at any time since the 1960s.

Much good that will do it under current management. There is no point in stacking up high-calibre ammunition if there are no guns to fire it. In Mr Major's day, there was an insoluble problem. The party would not follow its leader. Now, it only lacks a leader worth following. That is different. That is curable.

It is late in the Parliament to make such a change, yet there is no alternative. Though the voters may be unimpressed by the Tories' travails, they are bound to prefer a new leader to a broken one. Equally, the party could benefit from the increasing level of public apathy towards politics. As allegiances become more shallow, memories may become more short-term. It will be easier for a new Tory leader to efface bad impressions and project a fresh image than it would have been 20 years ago, in an era of more rooted partisanship and longer attention spans.

Even so, the quicker the better. If IDS were capable of thinking straight, he would now realise that there is one sole service which he could perform for his party, and for himself: to abdicate with dignity. Most sensible Tories hope that the Mawer report will produce a double headline: "IDS exonerated - and resigns." That would be the best possible outcome. But it seems a long time since the Tory party went in for best outcomes.