Duncan Smith's day began badly - and then it got worse news

The fateful message that could destroy Iain Duncan Smith's political career came at 10.30am, when the Leader of the Opposition walked upstairs to Sir Michael Spicer's second floor office in the shadow of Big Ben to hear the news he had been dreading for weeks.

The chairman of the Tory 1922 Committee had telephoned asking him for a meeting. When Mr Duncan Smith arrived, Sir Michael told him that he had received the crucial 25th letter calling for a vote of confidence in the leadership.

What could be Mr Duncan Smith's final full day in his job started badly at 8.10am when the former Shadow Chancellor Francis Maude announced that he had sent in a letter. This is rumoured to have been a secret trigger for a group of MPs opposed to Mr Duncan Smith to dispatch letters of their own. Such was the early morning ferment in Tory ranks that one journalist ran into two MPs carrying letters for Sir Michael in car park underneath the Palace of Westminster.

The veteran backbencher Sir Patrick Cormack became the first member of the 1922 Committee executive to call for the leader to submit to a ballot of MPs. He described the Tory leader as "civilised, polite, friendly and not bombastic".

For Mr Duncan Smith it was outwardly business as usual. Surrounded by his closest aides he spent nearly three hours preparing for the most important Prime Minister's question time of his political life. No one outside the inner circle was aware of the momentous events of a few hours earlier.

But at 12.30pm, senior members of the Shadow Cabinet were called to an emergency meeting. Michael Howard, the Shadow Chancellor, Oliver Letwin, the Shadow Home Secretary, Theresa May, the party chairman and Michael Ancram, the deputy party leader, were all present, as well as two further Shadow Cabinet members who have not been identified. A key absentee was David Davis, the Shadow Deputy Prime Minister, a man mistrusted by Duncan Smith loyalists and seen as a potential leadership hopeful.

Mr Duncan Smith told his colleagues he would address his backbenchers today and then submit himself to an immediate vote of confidence. Mr Howard and Mr Letwin joined Mrs May and Mr Ancram, all seen as potential leadership candidates, in offering to sign a letter of support for their leader.

At 1.50pm pagers belonging to the 12 Conservative whips buzzed with a "crash call", the emergency alert used to scramble party enforcers to deal with a crisis in the Commons. The message summoned them to a meeting in the office of David Maclean, the Chief Whip, who told them the confidence ballot had been triggered. At 2.15pm Mr Maclean authorised a second message to break the news to Tory MPs.

As the message went out, a member of Mr Duncan Smith's inner circle approached journalists in the members' lobby. He said: "You should be at Conservative Central Office in five minutes." Pandemonium broke out in the packed Press Gallery canteen, as political editors abandoned their prawn gumbo and ran for the exit.

Within minutes, Iain Duncan Smith came out, flanked by his wife Betsy and accompanied by Michael Howard, Oliver Letwin, Michael Ancram and Theresa May. He made a brief statement promising to hold a confidence vote after addressing backbenchers at today's meeting of the 1922 Committee.

Mr Duncan Smith said: "All of you gathered will know that yesterday I called on the parliamentary party to end this ludicrous leadership speculation that has been going on for the past few weeks. I said to end it by Wednesday. I can therefore say today that I am pleased that we will have an opportunity to do that tomorrow."

A joint statement, issued by all four senior figures, insisted he had "earned the right" to lead the party into the next election. Friends of the Tory leader said two junior Shadow Cabinet members who had been briefed by Mr Duncan Smith had not put their names to the statement, but predicted that senior frontbenchers would make their own statements during the afternoon. Mr Davis later rushed back to the Commons from lunch and demanded that his name was added to the frontbench declaration of support. Within minutes of Mr Duncan Smith's statement, a large group of Tory MPs gathered in the members' lobby of the Commons. Wreathed in smiles, they swapped jokes and gossip, excitedly guessing the next turn of events. A whip punched the air, and one MP talked about cracking open the champagne; while a long-standing critic of IDS grabbed a passing Tory woman MP for an impromptu waltz.

An overwhelming sense emerged that Mr Duncan Smith was entering the final few hours of his leadership. Tories of all shades of opinion also agreed that a narrow victory would not be enough to save him. One left-leaning MP said: "Fifty per cent plus one won't be enough. That would be a pyrrhic victory. A view will emerge as to what the required level of support is." A shadow minister, who backed Mr Duncan Smith two years ago, said: "I'm surprised he is even bothering to fight. He won't be getting my support again."

Sir Teddy Taylor, a strong supporter of Mr Duncan Smith, shook his head in disbelief at the turn of events, lambasting the "group of people out to destroy him". But he agreed that the leader would need a convincing vote of support. He said: "It's got to be a decisive result if we're going to have the strength needed in the leader of the opposition."

A lieutenant in Michael Portillo's failed leadership attempt two years ago said: "He isn't being brave. He is being stupid. It's another of the personal failings that have doomed his leadership." He said his constituency chairman had told him not to hand in a letter demanding the confidence vote - but was now under orders to give Mr Duncan Smith the black spot.

As MPs digested the news, rumours started about possible leadership campaigns. Reports of a clandestine evening meeting between Michael Howard and David Davis were strenuously denied, while some MPs clung to the hope that Kenneth Clarke could get Michael Portillo behind him in a last attempt at the leadership.

A group of 10 hardcore IDS loyalists formed a group attempting to rally Tories to their cause. They met small groups of backbenchers throughout the evening, warning that a leadership battle could see the party haemorrhage support in the country.

The Shadow Cabinet gathered as Big Ben chimed 3.45pm. Mr Duncan Smith won applause as he declared: "There's no tick box for you. I'm not trying to bully or push any of you to support me. You are individuals for the next 24 hours. You must do what you think is best."

Michael Ancram paid tribute to his colleague. Telling Mr Duncan Smith he spoke for the whole Shadow Cabinet, he said: "You faced the flak in the way all leaders do, but I have to say the flak you faced in the last few weeks has been unusually unpleasant. You have met it with dignity and courage."

The Shadow Cabinet broke into applause, banging their desks in appreciation. It is likely to be for the last time.

A Fateful Path Ahead

By Marie Woolf, Chief Political Correspondent

A lightning vote of confidence by Tory MPs will decide the fate of Iain Duncan Smith today.

But before his colleagues pass judgement on whether they want him to continue as party leader, Mr Duncan Smith will have to brave the House of Commons and face Tony Blair at Prime Minister's questions.

It could be the most high-pressure PMQs of his life, because only three hours later every one of his 164 parliamentary colleagues will have a chance to vote to get rid of him.

But before the polls open at 3:30pm today, Mr Duncan Smith will make a last attempt to win over doubting backbenchers. He will address a special meeting of the 1922 Committee of Tory MPs at 2:30, an hour before MPs vote.

In a committee room of the House of Commons, Mr Duncan Smith will make a final desperate plea to colleagues to support him.

Every Tory MP will have a right to vote, including absentees such as the two who are training in the Gulf as members of the Territorial Army.

They will be able to vote by proxy, possibly by e-mail or fax, while their colleagues file into the committee room.

Today's contest, which will be overseen by Sir Michael Spicer, chairman of the back-bench 1922 committee, will be all over by 6:30 pm when the secret ballot closes.

Iain Duncan Smith will find out whether he has got the votes necessary to preserve his leadership only half an hour later when the result is announced.

Officially, the beleaguered leader needs a simple majority of the votes cast to win. That is 83 votes if each of the 165 Tories who are entitled to vote participate.

But many Conservative MPs are expected to abstain, including those who have publicly pledged to support Mr Duncan Smith.

If he passes the winning post first, but only narrowly, it will be extremely difficult in practice for him to continue at the helm of the party.

If he does win convincingly, Mr Duncan Smith will continue as leader and his critics will be silenced for at least a year. The rules prevent another attempted coup for 12 months, in practice, until after the general election.

But if he fails, he will be forced to resign instantly and a leadership contest will be triggered.

That election would officially kick off with the proposal and seconding of candidates by Tory MPs. Sir Michael Spicer will act as returning officer for the leadership election.

If there is only one candidate, he or she will automatically be declared by acclamation as leader of the Tory party.

But if there is to be a contest between two candidates they will face an election among rank and file conservatives, following a series of hustings around the country. If more than two Tory MPs put their names forward there will be a run-off.

Conservative MPs will vote in a series of rounds for their favourite candidate and the least popular will be eliminated until there are only two left. It will then be up to the membership on the ground to choose a new leader from the two most popular candidates.