By Nick Assinder BBC News Online political correspondent

In an unprecedented move he has published 40 pages of the allegations levelled at the way he paid his wife to do secretarial work for him.

But, despite his categoric denials of wrongdoing, this will only add to his leadership woes.

The inquiry into the affair could last weeks and will inevitably hang over the Tory leader as the plotters now decide whether or not to move in for the kill.

Duncan Smith: Facing a challenge?

The fevered atmosphere of the Tory conference has transferred to Westminster where his plotters are stepping up their campaign to oust him before Christmas.

The truth is none of this will really change the plotters' calculations if they are determined on a course to remove IDS they will do that anyway.

His attempts to stop them in their tracks have so far proved fruitless.

And, despite all his tough talking, the plotters clearly believe that, if they can summon enough support for a challenge, he will eventually bow to the inevitable and stand down rather than pitch the party into a long, bloody and divisive election.

Martyrs

Threats to discipline those leading the plot may also have backfired, with the plotters believing it is they, not he, who are acting in the interests of the party.

They are perfectly within their rights, and the party's rules, to seek MPs' names for a possible challenge.

And dark warnings about what might befall them if they persist have not gone down at all well.

They have not forgotten that Mr Duncan Smith was a leading Euro rebel against former leader John Major.

He may not have plotted his downfall but they made his life hell.

And they still remember well what happened when Mr Major punished his Euro rebels - they became martyrs and the sniping continued.

So it now seems certain that the plotters are not about to give up.

Likely candidates?

They are actively seeking the 25 names needed to spark a contest and there is little to suggest that anything Mr Duncan Smith has done over the past week has changed that.

Equally, however, there is nothing to suggest the plotters are any closer to answering the key questions.

Firstly, can they actually gather 25 names to put before the Chairman of the backbench 1922 committee, Sir Michael Spicer to trigger a contest?

Second, have they got a candidate or candidates in mind as replacements and who they believe would fare better than Mr Duncan Smith?

The only thing all seem to agree on is that this threat to Mr Duncan Smith's position is genuine and serious and that the window of opportunity is closing

And third, are they confident they can ensure their candidate actually succeeds Mr Duncan Smith and that they would not end up with an election amongst Tory party members with other candidates putting their name forward?

That, after all, is how they ended up with Mr Duncan Smith, rather than Kenneth Clarke.

Lastly, and put bluntly, do they have the bottle to go in for the kill?

These are formidable hurdles to jump and that fact alone may be enough to persuade some dissenters not to put their names forward.

Others have clearly already decided that they will have to wait for Mr Duncan Smith to lose the next election before they can move against him.

The only thing all seem to agree on is that this threat to Mr Duncan Smith's position is genuine and serious and that the window of opportunity is closing.

If he survives into the New Year, he will almost certainly survive to the next general election.