Mr Duncan Smith called for an end to 'ludicrous leadership speculation'
Iain Duncan Smith says he will fight a vote of confidence in his leadership of the Conservative Party.
The poll comes after the Tory leader challenged plotters to get in line or submit the 25 names they needed to trigger a vote of confidence.
It was shortly after lunchtime on Tuesday that it became apparent the necessary number of letters calling for a confidence vote had been sent to the chairman of the 1922 committee, Sir Michael Spicer.
Mr Duncan Smith then appeared on the steps of Conservative Central Office, with wife Betsy, to welcome the chance to end weeks of speculation about his future as Tory leader.
He called on Tory MPs to back him in the vote - to take place on Wednesday - rather than plunge the party into a "fractious leadership election" which could last for months.
In a brief statement to gathered journalists Mr Duncan Smith dismissed any suggestion that he would quit rather than face a confidence vote.
"I will absolutely submit my name for a renewed mandate to lead the party to the general election and to win," he said.
"I say to my colleagues who will be responsible for making this decision tomorrow, that we have an unrivalled opportunity to take the fight to Labour at a time when they are failing.
"We should not now let the government off the hook by giving them this opportunity by plunging ourselves into a fractious leadership election that could last months and give the government the opportunity to escape proper scrutiny."
In a separate written statement, Mr Duncan Smith warned that a change of leadership would be "regarded with despair and contempt" by Tory supporters and would "gravely imperil" the party's prospects at the next election.
At the same time, four members of his shadow cabinet - Michael Ancram, Michael Howard, Oliver Letwin, Theresa May and latterly, David Davis - issued a statement of support for their leader.
TIMETABLE FOR WEDNESDAY
1200 GMT Prime minister's question time
1400 Deadline for proxy votes
1430 Iain Duncan Smith to address special meeting of Tory backbenchers who make up the 1922 Committee
1530 Confidence vote opens
1830 Vote closes
1900 Result is announced
They praised him for his "remarkable courage and dignity" under pressure, for his radical programme of public service reform and for making the Conservative Party "the champion of the people".
Mr Letwin later ruled himself out of any contest, saying that "under no circumstances" would he run for the leadership.
"I have said this over and over again for the last little while and eventually somebody will believe me that I am not going to contest the leadership of the Conservative Party now or ever," he said.
Mr Duncan Smith needs a straight majority of the votes cast by Tory MPs in the confidence vote to keep his post.
If he fails to get a majority of the votes he would lose his job, and is ruled out of the ensuing leadership contest.
Voting will take place on Wednesday between 1530 GMT and 1830 GMT. The result will be available about half an hour later.
About an hour before the voting begins Mr Duncan Smith is to address a special meeting of the 1922 Committee, which is made up of Tory backbench MPs.
Tory MPs who are unable to attend the ballot will be allowed to make their decision "by proxy" vote via fax, email or letter, provided these arrive before 1400 GMT.
Former government whip Derek Conway was the first Tory MP to publicly declare he had written to Sir Michael calling for a confidence vote.
He was swiftly followed by Crispin Blunt, who quit the front bench in May.
Former minister Francis Maude and Ryedale MP John Greenway declared their hands on Tuesday. Sir Patrick Cormack said he had written a letter after news of the leadership vote broke.