Work and Pensions Secretary Andrew Smith has resigned from the Cabinet to spend more time with his family and constituency.
Andrew Smith's resignation leaves a 'difficult' position to fill
BBC political editor Andrew Marr explains the background to his sudden departure.
Everybody was surprised by this. There had been all sorts of rumours, but no-one had been expecting this.
What it means is that Tony Blair is going to have to have a wider than expected reshuffle this week.
Andrew Smith was never one of the most glamorous, vivid or well-known members of the Labour Cabinet but he had a reputation as a quietly effective doer.
His work and pensions brief was a large and complicated one.
A major government report on the increasingly sensitive issue of pensions is only weeks away from publication and this department is the main victim of deep cuts in civil service jobs announced earlier this summer by the Chancellor - 30,000 jobs are to go by 2008.
But according to friends of Mr Smith his decision is closely connected to a recent row with advisers to Prime Minister Tony Blair about how radically benefits for disabled people should be targeted in a new crackdown.
Politics don't come much more unpopular than that.
Mr Blair wanted Mr Smith to stay and tried to persuade him to.
It leaves a major, difficult hole in government and bright, relative newcomers like schools standards minister David Miliband and Ruth Kelly are already being mentioned as possible successors.
Meanwhile, Downing Street is grappling with another difficult dilemma - how to bring back the Blairite ex-health minister Alan Millburn to beef up Labour's pre-election effort without terminally infuriating those already meant to be doing exactly that.
The holiday is over, the hangover has begun and a more extensive than expected government re-shuffle follows this week.