The Prime Minister’s announcement this afternoon that he intends to stand down triggers a complex election procedure to replace him and his deputy leader John Prescott, who is also retiring.

The first thing to note is that Tony Blair is still PM and will remain so until he goes to see the Queen on June 27th and resigns.

Her Majesty will then ask whoever has been elected by the Labour party as their leader to form a government.

On Sunday the National Executive Committee of the Labour party will instigate the process of electing the new leadership.

Nominations will open on Monday at 2.30pm and close on Thursday. Official candidates will be announced on Thursday ballots sent to the 380 Labour MPs and MEPs as well as 200,000 party members and 3.2m members of affiliated trade unions who pay a political levy.

On Sunday 20th July there will be the first husting event, which Gordon Brown is expected to attend even if he is standing unopposed.

Counting ballots starts on Monday 25th June.

Any candidate who wants to run for leader or deputy leader of the party first needs the backing of 12.5% of Labour MPs, at present that means 44 endorsements.

The party uses an electoral college to elect its leadership, split three ways between the MPs and MEPs, the party membership and members of affiliated unions. Nearly 3 million people will get a vote.

Any candidate that gets 50% or more of the vote wins outright, otherwise further elimination ballots will be held.

In the next few days Gordon Brown is expected to launch his campaign for leader.

He has already got the endorsement of well over half of Labour’s MPs.

The Chancellor is clearly the favourite to succeed though there is likely to be a challenge from a left-wing MP, either Michael Meacher or John McDonnell.

They have delayed a decision about which one of them will run until next week. It remains unclear if collectively they have the support of 44 MPs needed to become a candidate.

The race for deputy leader is much more of an open field.

Just hours after Mr Prescott’s public announcement he would stand down, Peter Hain announced he has the endorsement of 44 MPs.

As Secretary of State for Northern Ireland, Mr Hain pushed through the Sexual Orientation Regulations in the teeth of opposition from Unionist parties.

While Ruth Kelly delayed the regulations in the rest of the UK, Northern Irish LGB people benefited from their protection from January 1st.

The regulations, which outlaw discrimination against gay, lesbian and bisexual people when accessing goods and services, became law in Britain on April 30th.

“I am standing for the deputy leadership because I believe that in order to win the next election, Labour must reconnect the leadership of the party with grassroots members and trade unionists, reach out to those in society we have lost touch with, and rebuild the progressive coalition which secured us two landslide victories,” Mr Hain said.

Among his backers is Clive Betts, the Sheffield Attercliffe MP who was outed by The Sun in 2003, former Cabinet minister Paul Murphy, junior ministers Maria Eagle, Paul Goggins and Phil Woolas and renegade MP Bob Marshall-Andrews.

In March the Education Secretary, Alan Johnson, had his candidacy for the deputy leadership of the Labour party endorsed by a string of ministers.

Many of the middle-ranking MPs had warm praise for the tenacious way Johnson stood up to the Prime Minister in defence of gay equality laws.

In January Mr Blair and the Communities Secretary Ruth Kelly were at the centre of a cabinet row over anti-discrimination legislation.

They wanted to grant exemptions to the new Sexual Orientation Regulations to Roman Catholic-run adoption agencies.

Alan Johnson led the Cabinet’s opposition to the co-called Catholic tendency, phoning colleagues to canvass their views and vocalising the opinion of many Labour backbench MPs that equality legislation should never be amended to accommodate special interest groups.

Seven ministers have declared they back Mr Johnson to succeed John Prescott as deputy leader.

The ministers represent Blairites such as Pensions Minister James Purnell and ministers from a range of departments across the government.

As well as his clear-minded defence of equality, Mr Johnson’s CV speaks to the Labour party’s heart.

He began his professional life as a postman and rose to become the leader of the Communication Workers Union.

Bounced into a safe seat weeks before the 1997 general election, he became the first former union leader in 40 years to sit in Cabinet.

The support of Mr Purnell, who used to work as an adviser to Tony Blair, is seen as a key sign that Johnson’s bid for the number two job has really taken off.

Hilary Benn is a declared candidate for deputy leader but it seems unlikely that the International Development Secretary will survive in a race against Johnson and Hain.

There are already rumours he has not been able to find the backing of 44 MPs.

Harriet Harman, a declared candidate, also spoke up for the Sexual Orientation Regulations.

She entered the race because she thinks the Labour party “needs” a woman deputy leader.

Not a Cabinet minister, Harman is rumoured to be building her support amongst MPs.

Backbench candidate Jon Cruddas is busy touring the country with a message of grassroots renewal, and could have strong appeal to disaffected party members.

The influence of the MPs on the result makes it unlikely that Mr Cruddas will win, even if he gets every party member to vote for him.

The deputy leader of the Labour party is not immediately entitled to the title of Deputy Prime Minister, which is in the gift of the PM.

Mr Cruddas has argued that the deputy role should be separate from government, and that the deputy leader should concentrate on communicating with the party and repairing its grassroots.

Hazel Blears is a candidate, but as party chairman she has the responsibility of overseeing the process.

Her ultra-Blairite tendency to be ruthlessly on-message may not appeal to union or constituency Labour party members.

Her campaign website no longer offers people the opportunity to show support by buying a T shirt carrying the logo “Nuts About Hazel.”

According to www.hazelblears.com the garments were being produced by a company with a less-than ethical reputation in Bangladesh.

Other Cabinet members are rumoured to want the job but given the strength of Hain and Johnson’s positions it seems unlikely they will run.

Jack Straw was an early candidate, but is now running Gordon Brown’s campaign for leader. He is one of those tipped to be the next Chancellor.

Tessa Jowell, once the darling of the party, has been battered by storms surrounding her husband’s business dealings and the Olympics budget. A close ally of Tony Blair, she will be lucky to remain in Cabinet.

Gordon Brown is likely to be elected outright with more than 50% of the vote in the first ballot.

It is likely therefore that he will be elected before his deputy. But the deputy will finally be decided on the same day by a process of elimination.

In any case, the next leader of the Labour party will be at Buckingham Palace on 27th June to take office as the party’s sixth Prime Minister.