By Nick Assinder BBC News Online political correspondent

Mr Duncan Smith remains defiant

Throughout this crisis he has suggested his detractors do not have the courage to face him, eyeball to eyeball.

Now, with fears the affair is doing the party incalculable damage, he has sought to end it - one way or another.

Setting an artificial deadline is risky as it offers the rebels the option to flout his authority, further undermining his leadership.

But many might think it is also a canny move to finally call their bluff.

High Noon

Mr Duncan Smith has now spoken to scores of his backbenchers. He may not have learned much from them, but they will have been delivered the clearest possible message from him.

And that is: "If you are one of those whispering behind my back: it's High Noon time."

If the plotters now fail to act by the time of the all-important meeting of the 1922 committee on Wednesday night, he calculates they will look weak, undisciplined and afraid or unable to strike.

Mr Duncan Smith clearly hopes his tactic will reveal them as the small group of bitter malcontents he believes them to be.

It's quite a gamble - if they are a genuine and organised threat, they now have no alternative but to act.

For good or ill, the leadership crisis which seems to have dogged him almost since the day he was elected should be resolved within the next couple of days.

Game of bluff

The plotters still appear to be facing the dilemma of deciding who they want to replace Mr Duncan Smith, and how to avert a poll of grassroots party members.

There are some signs, however, that they may be close to resolving the first problem, with Michael Howard's name being bandied about - without any encouragement from him, it must be said.

If they get the 25 names needed to spark a confidence vote, and if the leader refuses to stand aside, many are convinced that Mr Duncan Smith would lose.

What is unclear is whether Mr Duncan Smith agrees with that assessment and is simply engaged in a game of bluff in saying he would fight on - or does he really believe he could win a confidence vote?

HAVE YOUR SAY IDS - he is the absolute personification of just how irrelevant the Conservatives have become Robert Crosby, UK Send us your comments

Of course it is possible he could win a vote. There are plenty of backbenchers seething at the way the plotters have promoted this crisis.

If a leadership vote was sparked and IDS won it, his position would be hugely emboldened. But, for most people, such an outcome is seen as a long shot.

The plotters' hope appears to be that, once it gets to a leadership poll, MPs will be so eager to avoid another vote of grassroots party members they will finally rally behind one candidate they perceive as a winner.

Given the years of faction fighting in the Tory party, some may see that as wishful thinking.

Either way, things have now clearly passed the point of no return.

Even those who do not particularly want a leadership election believe the plotters' destabilising tactics have been so successful that they must now end the murmurings one way or another.

That group is now led by Mr Duncan Smith himself.