Mr Duncan Smith cannot go on like this and nor will he be allowed to do so

He will either resign or be ousted. The option of just limping on as leader into the next election vanished this week

Iain Duncan Smith is a weak leader in a weak position. That is a pretty desperate situation for himself and his party, but not necessarily a fatal one. Both the main parties have at different times been saddled with weak leaders who have staggered on for years. What is fatally different now is that Mr Duncan Smith affects to be a strong and defiant leader when he should be tiptoeing deftly around the landmines. Yesterday he issued an ultimatum to his warring party: "Unite or die." His problem is that too many of his MPs have reached the conclusion that they will die under his leadership.

Of all the surreal entertainment laid on by Conservative leaders in recent years yesterday's "personal statement from Mr Duncan Smith" was the most absurd. That is quite an achievement. The Conservatives have given us: John Major standing down as leader, but staying on as Prime Minister, to fight a leadership contest although no one had issued a challenge; the "dream ticket" in 1997 of Ken Clarke and John Redwood when one wanted to join the euro and the other wanted Britain to leave the EU; and William Hague donning his baseball cap and exuding compassion before acquiring a crew cut. Now step forward Mr Duncan Smith, who yesterday cancelled a press conference on housing without telling all his colleagues. At the same time journalists were summoned to Conservative Central Office assuming an act of great drama was to unfold. In the event, Mr Duncan Smith merely chose to highlight the turmoil in his party, and in doing so made that turmoil much worse. Thank you and good night.

The leaders and potential leaders do not function in a vacuum. They behave oddly partly because there is something odd about the Conservative Party. It is by no means all down to their own eccentricities. But in this particular case it is Mr Duncan Smith himself who has contrived to get into such a silly and precarious situation. That is what makes the current situation so dangerous for him. In the Shadow Cabinet meeting the week before last, he led the calls for the imposition of a three-line whip on the proposals to allow unmarried couples to adopt. It was Mr Duncan Smith again yesterday who compounded the original error by claiming that those who rebelled were acting out of personal ambition rather than conviction.

This intervention was disastrous for two reasons. Firstly he is wrong. I had known for several days that John Bercow was considering resigning from the Shadow Cabinet over this issue. It was only on Sunday evening that he finally made up his mind after a week of agonising over what to do. I am convinced that he resigned because he felt strongly about the right of unmarried couples to adopt and the backward-looking signal opposition to that right sent out to the wider electorate.

Similarly, after all Michael Portillo has said about the importance of modernising the party, he had no choice but to rebel on Monday night. I believe Mr Portillo when he says he does not want to be leader. He and some of the other rebels would not shed a tear if Mr Duncan Smith was no longer leader, but they were not actively conspiring to bring this about on Monday.

This was Mr Duncan Smith's second mistake. He has made last Monday's revolt seem more sinister than it was. By attempting to appear strong, he has made himself weak.

This has been the running theme of his leadership. The inept sacking of David Davis as party chairman last summer was mishandled for the same reasons as this week's shambles. A day after the reshuffle that knifed Mr Davis, one of the leader's aides told me: "This shows no one messes with Iain." But it was "Iain" who ended up in a mess. The decision to impose a three-line whip on last Monday's vote was taken partly because it would have appeared "weak" to allow a free vote when a three line whip had been imposed on the same issue in the past.

Yesterday there were conscious echoes of Neil Kinnock as Mr Duncan Smith warned his party against "self-indulgence", a phrase Mr Kinnock often deployed in his own internal battles. But Mr Kinnock battled with some sense of clear purpose. When he raged against Militant there was an obvious next step – the expulsion of Militant and some recovery of Labour's standing in the polls. Yesterday's statement did not lead anywhere very precise, or anywhere at all beyond another Conservative leadership contest.

Conservative leaders are haunted by Tony Blair's famous soundbite that so wounded John Major in the mid-1990s. The words "I lead my party. You follow yours" whirl around their heads like a painful drill. Ever since Mr Blair uttered the soundbite Messrs Major, Hague and Duncan Smith have tried to show that they can lead rather than follow. But Mr Blair was in an unusually privileged position in the mid-1990s of leading a party that was willing to be led, hungry for electoral success. Mr Duncan Smith is in a different position in that he leads a parliamentary party hungry for mere survival.

He makes much of his support in the constituencies, but every Conservative leader enjoys loyalty at grassroots level. At the nadir of John Major's premiership, he had huge support amongst activists. So did Mr Hague, whose entire leadership was a nadir. The only clever part of yesterday's bizarre strategic manoeuvring was to remind any potential rival that Mr Duncan Smith won the leadership by a landslide in the constituencies and would do so again if a contest was held tomorrow. In the end, though, it is MPs frightened of losing their seats who will shape the political context. To an extent they've already shaped that context and it will not change now.

Mr Duncan Smith has made some progress in terms of policy. The party conference – apart from his own dreadful speech – was in my view the most challenging to New Labour since Tony Blair won the leadership in 1994. But that is already a distant memory. Mr Duncan Smith now finds himself in a position where this afternoon's Prime Minister's Questions will be seen for the second week running as another vital "test" of his leadership. Then it will be his response to the Queen's Speech a week today. Meanwhile every word uttered by other senior Tories will be monitored for a whiff of dissent. This is not sustainable for long. More to the point, Conservative MPs from across the party recognise this is not sustainable.

There is one alternative to a vote of no confidence from despairing MPs. He once said that a leader's image is established in the first 18 months. Close to his chosen timescale he is associated with ineptitude and unrest. His army background has given him a resilience that will make resignation unpalatable. But commanders with integrity do not lead troops to the abyss if an alternative leader has a chance of saving some of their skins. The Conservatives are getting very close to the abyss.

Mr Duncan Smith will either resign or be ousted. The option of limping on as leader into the next election vanished this week.