Five scenarios for the Prime Minister: from immediate departure to going on and on

BLAIR GOES THIS MONTH

Scenario: More ministers resign in protest at Tony Blair's failure to name a date. Mutterings among previously loyal backbenchers intensify, with rebellion also growing ahead of this month's party conference among constituency parties. Gordon Brown authorises key lieutenants to strike the final blow by telling Mr Blair to resign as soon as possible.

What happens next: Mr Blair uses his conference speech on 26 September to announce his resignation, setting the process in train for electing a new leader by late November.

Likelihood: Would have seemed wildly improbable just days ago, but the turmoil over the past 48 hours has shortened the odds.

BLAIR GOES THIS YEAR

Scenario: Blair's critics call an uneasy truce for three weeks, hoping he makes an explicit declaration of his plans from the conference stage. But he disappoints them by confirming he will be in Downing Street until the summer of 2007. Fury breaks out at the conference and the mutiny grows when MPs return to Westminster.

What happens next: Mr Blair realises his position is untenable and the message is reinforced by Cabinet ministers and senior representatives of the Parliamentary Labour Party.

Likelihood: Possible. If the PM does not have his party's support for the programme outlined in the Queen's Speech in November, he is doomed.

BLAIR GOES IN THE SPRING

Scenario: Mr Blair makes it through a fraught party conference and autumn parliamentary session, but only just. As Labour's poll ratings refuse to pick up, and the party faces meltdown in next May's elections in Scotland and Wales, the rumblings begin again. Brownite Ministers make less effort to mask their frustration over the Prime Minister's intransigence.

What happens next: The gloom in the Downing Street bunker is mirrored by the insurrection among grassroots activists. Mr Blair bows to the inevitable in January, announcing a new leader will be in place by Easter.

Likelihood: Until recently, most of Mr Blair's critics would have settled for his departure in early 2007. Now they are working to a shorter timetable.

BLAIR GOES IN THE SUMMER

Scenario: Mr Blair averts his immediate crisis with a barnstorming conference speech that makes it plain he is on the final lap of his premiership. Labour's standing in the polls stabilises. Gordon Brown, reassured that his day of destiny is finally in sight, demands scrupulous loyalty to the PM from his acolytes. The last thing he wants, he tells them, is to inherit a party racked by internecine strife.

What happens next: The Prime Minister resigns in May, paving the way for the Chancellor to take over two months later. Alternatively he could announce his resignation in July, with a new leader unveiled at the Labour conference.

Likelihood: The chances of Mr Blair hanging on that long are fast receding.

BLAIR GOES ON - AND ON

Scenario: A storming conference speech and an eye-catching Queen's Speech reassure the party that there is plenty of life left in Tony Blair. The Tories seem stalled under David Cameron and Labour MPs begin to be more optimistic about the prospect of a fourth election victory. The upturn in the party's fortunes are confirmed by much stronger performances than expected in Scotland and Wales in May.

What happens next: Mr Blair confounds colleagues, including cabinet allies who had promised he would be gone by the middle of 2007, to announce he is staying on.

Likelihood: Impossible - the dream outcome for Blairite "ultras".

Nigel Morris