Tony Blair will tomorrow announce he is standing down as Labour leader after a decade in Downing Street, paving the way for Gordon Brown to succeed him as Prime Minister.

Mr Blair will first tell Cabinet colleagues of his intentions at their regular 9am Thursday meeting at No 10, then travel to his Sedgefield, Co Durham, constituency to make a public pronouncement.

The Prime Minister's official spokesman ended weeks of speculation by saying tonight: "There will be a Cabinet tomorrow morning at 9 o'clock. I don't think that will be quite as long as usual.

"The Prime Minister will then go elsewhere to make an announcement and that will be all that happens.

"There will be nothing said in Downing Street."

Mr Blair remains as Labour leader until his successor is formally elected at a special party conference, and as Prime Minister until he hands in his seals of office to the Queen.

Labour's National Executive Committee will meet within 72 hours of tomorrow's confirmation to draw up a detailed timetable for an election to replace both Mr Blair and his deputy John Prescott, who has already announced he will quit at the same time as the Prime Minister.

The whole election process will take about seven weeks, meaning Mr Brown - if he is elected - will take office some time in early July.

He is likely to face only a token left-wing challenge from either backbencher John McDonnell or former minister Michael Meacher.

The two will announce tomorrow which of them is to try to stand against the Chancellor.

Downing Street insisted today the Prime Minister would not be a "lame duck" leader while his successor is being elected.

But Tory leader David Cameron mocked his administration as "a Government of the living dead" during a rowdy Prime Minister's Question Time in the Commons.

Mr Blair retorted he would focus on domestic policy issues over the coming weeks, but he is also expected to embark on a round of whistlestop diplomacy ahead of next month's G8 and EU summits.

He is almost certain to travel further afield as well, but Downing Street never speculates on the Prime Minister's future travel plans, citing security concerns.

Mr Cameron said Mr Brown was preparing to sack a series of ministers.

He singled out Foreign Secretary Margaret Beckett, Health Secretary Patricia Hewitt and the new Justice Secretary Lord Falconer, who he said were "for the chop".

Mr Cameron told MPs: "The Chancellor's spin doctor is walking round the lobby handing out their jobs.

"This is the Government of the living dead. Why do we have to put up with it?"

Mr Cameron claimed there would be "another seven weeks of paralysis".

Mr Blair, flanked by Mr Prescott and Mr Brown, hit back: "I'll tell you what I will be concentrating on in the next seven weeks and that's policy, the policies on education and health and law and order."

The Prime Minister's official spokesman had earlier responded to suggestions of a lame duck premier by saying: "The best reassurance you will have is actually seeing the Prime Minister in action.

"And I think you will see the Prime Minister in action over the coming weeks, both domestically on issues such as health and education and also internationally - particularly in the run-up to the G8 summit and in the run-up to the EU summit, both of which are very important events.

"I don't think people would be left in any doubt that the Prime Minister is fully engaged, but rather than me saying it, the best thing is simply for people to watch and see."

Germany holds the rotating presidency of both organisations and will host the gatherings next month.

Mr Blair is keen to pursue his Gleneagles agenda of climate change and helping Africa at the G8, while the EU meeting will attempt to break the deadlock over the union's constitution.

"In terms of getting on with business, Europe does face major decisions and he believes you can work with other leaders in Europe to achieve that," added the Prime Minister's spokesman.

Despite Downing Street's determined "business as usual" stance the coming weeks are bound to be dominated by debate over Mr Blair's legacy to the country and his plans for the future.

No 10 has insisted he has made "no decision whatsoever to stand down as an MP" and dismissed various reports of Mr Blair either setting up foundations or acting as a roving ambassador in the Middle East and Africa as speculation.