Tony Blair will resign as Labour leader tomorrow and is expected to endorse Gordon Brown as his successor.

The Prime Minister returned from the restoration of the Northern Ireland Assembly in Belfast last night to prepare for today's Prime Minister's Questions and tomorrow's resignation statement but last night Downing Street refused to be drawn on the details of his plans.

Mr Blair will not stand down as Prime Minister until his successor is elected to the Labour leadership, likely at the beginning of July.

Tomorrow, Mr Blair is expected to inform the cabinet of his intentions, and speculation suggests he will then fly to his Sedgefield constituency to make a public statement and thank party workers for their support and help.

Mr Blair has not disclosed whether he intends to stand down as an MP. Close allies believe that is what he would like to do but some have counselled him against causing a by-election.

Gordon Brown, the runaway favourite to succeed Mr Blair, is expected to make a speech on Friday. While it is not yet known if he will face a challenge, Mr Brown intends to tour the country spelling out his prime ministerial agenda.

His task is not without its difficulties since he has to lay out a new direction of travel without appearing to be disloyal to the Prime Minister and the government in which he has played a pivotal role for its duration.

Mr Blair will have his weekly audience with the Queen in Buckingham Palace tonight and while it is inconceivable that he will not discuss his future plans with her, his spokesman revealed yesterday that there was no constitutional requirement for the Prime Minister to tell the monarch in advance of his intention to step down as party leader.

Labour's ruling National Executive Committee has laid down a seven-week process to elect successors to Mr Blair and his deputy John Prescott, who intends to step down at the same time.

Candidates with 45 nominations will go forward to the final ballot.