The qualifying number of 25 Tory MPs have now called for a vote of confidence in the party leader Iain Duncan Smith.
Mr Duncan Smith said that he would fight on. He would stand for the vote and "put an end once and for all to the speculation that has been sapping this party".
He has agreed with Sir Michael Spicer, chairman of the backbench 1922 Committee, that the confidence vote should be held at tomorrow's meeting of the committee - immediately after the Conservative leader has spoken to backbench MPs. The result is expected about 7pm.
"I will absolutely submit my name for a new mandate to lead the party to the general election," he said outside party headquarters, with his wife Betsy at his side.
The surprise announcement that 25 MPs had already called for the vote came this afternoon hours after a former minister today became the most senior Tory so far to declare publicly that he has called for a vote of no confidence in the Tory leader.
Francis Maude said he had written to Sir Michael Spicer and urged others to follow his lead.
Mr Maude, a former Treasury minister who was shadow chancellor under William Hague, made his declaration in an article for London's Evening Standard newspaper. He said: "I put my cards on the table. I have formally asked for a vote of confidence to be called.
"Personally, I believe we would do better under a different leader and I will vote accordingly if a ballot is triggered," he said.
He was immediately followed by John Greenway, the Ryedale MP who left Mr Duncan Smith's shadow cabinet in June.
Mr Greenway became the fourth Conservative MP to declare publicly his call for a vote of confidence in Mr Duncan Smith's leadership, saying: "For the sake of my party and for the sake of my country, I believe we have to have a vote of confidence."
A fifth MP then joined the list. He told PA News, on condition of anonymity, that he had added his name to the list of MPs challenging the leader's position.
Hours later came the announcement from a party official that 25 letters had been received - enough to trigger the vote.
Mr Duncan Smith raised the stakes yesterday in his battle to remain Tory leader by giving his critics 48 hours to force the vote or call a halt to plotting against him.
In a seemingly final attempt to shore up his position, the Conservative leader declared he would appear before the backbench 1922 Committee tomorrow and make a direct appeal for his MPs' support.
Mr Duncan Smith claimed that if the required 25 MPs had not come forward to demand a vote of confidence by then, the party should draw a line under the affair and unite behind him.
Mr Maude, MP for Horsham, interviewed on BBC Radio 4's Today programme, was asked whether it was his sense that the majority of Tory MPs want a change of leadership.
He replied: "Yes it is. But I can't demonstrate that. I have only talked to a very few people but there is a sense that the concern is very widespread. Iain and his team may be quite right that this is just a few malcontents. I don't think that that is right, but this is an opportunity this week to show one way or the other.
"If there is widespread concern then a vote will be triggered and we can go through the duly laid down process. If not then we must rally behind Iain and endeavour to make a success of his leadership," Mr Maude said.Reuse content