Former children's secretary Ed Balls is set to become the latest candidate to throw his hat into the ring to succeed Gordon Brown as Labour leader, it has emerged.

It is expected that Mr Balls - long regarded as Mr Brown's closest lieutenant in the Cabinet - will formally declare his candidacy later today.

He will join brothers David and Ed Miliband - the former foreign and energy secretaries - who have already declared they will be contenders in the race for the Labour crown.

Left-wing Labour MP John McDonnell is expected to announce later that he also intends to stand.

Mr McDonnell, who retained his Hayes and Harlington seat at the General Election, will launch his campaign at the annual conference of the Public and Commercial Services Union in Brighton.