Labour will now go through a leadership contest later this year following the announcement that Gordon Brown is to resign.

David Miliband emerged as early favourite to take over according to the bookmakers. The Foreign Secretary is the front-runner in the Labour leadership contest with the bookmakers Paddy Power, William Hill and Ladbrokes.

However, Schools Secretary Ed Balls, a close ally of Mr Brown, is close behind.

Energy Secretary Ed Miliband, David's brother, is also a contender to gain the Labour leadership - while Home Secretary Alan Johnson is also in contention.

Leader of the House of Commons Harriet Harman and Chancellor Alistair Darling are also tipped as possible runners.

In order to take part in the leadership contest, candidates must be current members of the House of Commons and must secure the backing of 12.5% of the party's MPs, which equates to 33 supporters following last week's election.

Labour said that rule changes since the 1994 contest meant that around 3.2 million people will be entitled to vote in this year's leadership election.

Here STV News looks at some of the runners and riders.

David Milliband: The 44-year-old Foreign Secretary has emerged as an early favourite, and is hotly-tipped within Westminster as the next Labour leader.  The Oxford graduate was made Tony Blair's Head of Policy in 1994, before being elected to Parliament for the first time in 2001 in the South Shields constituency, which he still holds today.

Ed Balls: Currently Schools Secretary, the 43-year-old represents Morley and Outwood.  He is said to have the backing of the powerful unions and is known to be loyal to Gordon Brown. A Labour member since the age of 16, he was first appointed as an economic advisor to Mr Brown in 1994, and took office for the first time at the 2001 election.

Ed Miliband: The youngest of the potential leaders, Ed Miliband - younger brother of hot favourite David - is currently Climate Change Secretary, and has been MP for Doncaster North since 2005.

Alan Johnson: An experienced campaigner, Johnson has been MP for Kingston upon Hull West and Hessle since Labour swept to a landslide victory in 1997. Popular with the public for his down to earth manner, but could be hampered after previously insisting he did not want the top job.

Harriet Harman: The long serving MP - member for Camberwell and Peckham since 1982 - is currently deputy leader of the party and is known for her strong views on equality. She once wore a stab vest while touring her London constituency under police guard, but is something of a divisive figure among certain sections.

Alistair Darling: The 56-year-old Chancellor of the Exchequer is MP for Edinburgh South West.  Is seen as a trusted parliamentarian and a safe pair of hands - but could be tainted by being in charge of the Treasury during the worst recession in living memory.