Rebel Tory MPs are predicting "humiliation" for Mr Iain Duncan Smith today if he persists in fighting a confidence vote in his leadership of the British Conservative Party.
The embattled Tory leader has vowed not to quit and is scheduled to address his MPs at Westminster this afternoon just before their sudden-death vote on his political future.
Many more than the required 25 MPs yesterday called their leader's bluff and submitted letters demanding today's confidence vote. If their challenge succeeds by a simple majority the Conservative Party will tonight be in the throes of its sixth leadership contest in 14 years.
Appearing on the steps of Conservative Central Office with his wife Betsy, Mr Duncan Smith said he welcomed the chance to renew his mandate to lead the party into the next general election. The embattled Tory leader also had the public backing of senior members of his shadow cabinet including three - Mr Michael Howard, Mr David Davis and Mr Michael Ancram - strongly tipped to enter any succession race.
However for all his public defiance it was clear "IDS" and his central office command had been taken by surprise as "the plotters in the shadows" accepted his challenge to make this the day of decision.
Even as he issued that challenge on Monday afternoon, Mr Duncan Smith predicted that the requisite 25 signatures would not be forthcoming. And that confidence was again evident yesterday morning when Mr Michael Portillo's former campaign manager, Mr Francis Maude, became only the fifth MP to publicly call for a clear-the-air vote.
Front-bench spokesman Mr Tim Collins said Mr Maude's "outing" of himself as one of the plotters was evidence of their increasing desperation and again insisted the threatened challenge would not materialise.
Mr Duncan Smith learned soon after this that it had and the desperation was evident last night in the leader's camp as large numbers of Tory MPs predicted IDS would soon be "toast" and that his refusal to stand-aside could result in "humiliation".
However there were conflicting assessments from still-loyal MPs as central office sought to swing doubting backbenchers by way of pressure from the constituency parties which overwhelmingly backed Mr Duncan Smith to succeed Mr William Hague two years ago last month.
Confirming that he would face the members of the backbench 1922 Committee to state his case, a defiant Mr Duncan Smith told reporters: "(On Monday) I called for the parliamentary party to end the ludicrous leadership speculation that has been going on for the past few weeks. I said to end it by Wednesday. I can therefore say that I welcome and am pleased that we will have an opportunity to do that."
Mr Duncan Smith is due to address the 1922 Committee at 2.30 p.m., with MPs then voting between 3.30 p.m. and 6.30 p.m. and a result is expected by 7 p.m.