The mood among Tory MPs is black - for many it is worse than Thatcher's last days

When Iain Duncan Smith told last month's Tory conference not to underestimate "the determination of a quiet man," the party faithful loved it. "They got the message," a relieved Tory leader told aides later.

Sadly for Mr Duncan Smith, the voters and his own MPs did not. Only four weeks after the conference and just over a year in the job, the Tory leader is fighting for his political life.

His dramatic warning yesterday that the Tories must "unite or die" was probably his last throw of the dice. He can only make such an appeal once, and last night there was little sign of it being heeded. His hastily arranged press conference looked more like an act of weakness than strength – it is hard to imagine Tony Blair pleading with party rebels.

The mood among Tory MPs last night was black; for some, the atmosphere was worse than in the final days of Margaret Thatcher's reign. Mr Duncan Smith's ploy may not give him the breathing space he wanted but only reinforce doubts about him in his own ranks. "He is finished," said one senior MP. Another rolled his eyes and ran his finger across his throat in his verdict on the leader's prospects.

The Bournemouth conference appeared to go relatively well. Mr Duncan Smith feared it would be overshadowed by John Major, Edwina Currie and Jeffrey Archer. In the event, the Tories were able to focus on some new policies. Aware that he was still unknown to many voters, Mr Duncan Smith sought to raise his profile by going on a three-week nationwide tour. He received positive coverage in the local and regional media. But the tour played badly at Westminster: his MPs began to complain that he was invisible.

The grumbling got louder when he put in three poor Commons performances. On Monday last week, he even made a crass mistake by suggesting that Mr Blair was under threat from Gordon Brown. Mr Blair replied with some "free advice" not to raise the issue of leadership.

The conferences usually give parties a boost. But the "quiet man" made no impact in the real world. An ICM poll showed Labour extending its lead to 11 points, while Mori found that most people – and even Tory supporters – were not satisfied with his leadership.

The polls reinforced the sense of crisis among Tory MPs. Last week, Mr Duncan Smith's critics let it be known that they had the 25 names necessary to force a vote of confidence.

Interviewed by The Independent last Thursday, he dismissed his critics as "a few MPs with disagreements" and said he "couldn't care less". But that strategy was no longer tenable after Monday's Commons rebellion over the party's hard line against plans to allow unmarried couples, including gays, to adopt.

The bizarre decision to impose a three-line whip rather than allow a free vote provoked the resignation from the Shadow Cabinet of John Bercow, a leading moderniser. Michael Portillo and Kenneth Clarke, a possible dream ticket for the leadership, defied the three-line whip. Mr Duncan Smith realised that the vultures were hovering; he had to do something to stop the rot.

The Tory leader decided first thing yesterday to make his last-gasp appeal for unity. As the first Tory leader to be elected by the party's 350,000 members, he judged he had only one "lever" at his disposal: to urge local parties to put pressure on the MPs undermining him.

So his "personal statement" was directed at Tory party members rather than the public or his MPs. His problem is that under party rules, it is the MPs who decide whether there is a leadership contest. Their fingers are on the trigger, and it may not be long until they pull it.