By Nick Assinder
Political correspondent, BBC News website
If Gordon Brown wants a Tony Blair-style "new dawn" to usher in his premiership, John Reid's resignation is a symbolic first step - and there may well be more to come.
John Reid has not enjoyed a close relationship with Mr Brown
While the next prime minister will undoubtedly need to heal the rifts caused by Mr Blair's early retirement and subsequent leadership squabbles, and move on from the drubbing in last Thursday's elections, the voluntary redundancy of key Blairites like Mr Reid will make that job far less troublesome.
It will help leave the field clear for Mr Brown to cast a new-look team in his own image and may even mark the beginning of a withdrawal from the front line of the so-called "ultra Blairites" some had predicted might give the new prime minister problems.
There have already been rumours that Mr Blair, Mr Reid and loyalists Stephen Byers and Alan Milburn were planning to quit as MPs - even that they might do so before the next election, so sparking by-elections.
The prime minister's spokesman has insisted Mr Blair has made no such decision and should that group of four, or more, take such a path it would cause huge anger and resentment in the party and lead to claims the Blairites were abandoning Labour in a fit of pique.
It would also see claims the prime minister had never seen himself as a Labour Party man but more a presidential figure and was now more interested in his future, more lucrative career on the international lecture circuit.
However, there is a real sense of change in Westminster at the moment and it would be foolhardy to rule anything out, no matter how apparently unlikely.
What now seems absolutely certain is that Mr Brown will not face a heavyweight Blairite challenge to his succession.
A host of possible candidates have ruled themselves out - Alan Johnson, Alan Milburn, Charles Clarke, David Miliband, John Hutton and now John Reid.
So the only men now left standing are left-wing backbenchers Michael Meacher and John McDonnell, and it remains to be seen if they can muster enough support to allow one of them to press ahead.
That question - along with others concerning the Blairites, perhaps - will be answered shortly after the prime minister makes his resignation announcement next week, possibly on Thursday.
As for John Reid - who has held nine frontbench jobs over the past decade - his statement came as a surprise to just about everyone in Westminster despite the widespread belief he had already decided not to challenge Mr Brown.
It is certainly the case that the two men were not friends, indeed Mr Reid's opposition to Mr Brown was verging on the legendary and the home secretary had previously joked he might end up as Mr Brown's tea boy after the succession.
But there had also been persistent speculation the chancellor was planning to leave him at the crisis-hit home office to see through his reforms and their aftermath.
Those reforms, centred around splitting the department in two, are proving highly controversial and handling that will now fall to whoever Mr Brown appoints to the job.
What the chancellor will desperately not want to see is any heavyweight figure such as Mr Reid sniping at him from the backbenches.
However, if the recent statements from Mr Reid, Mr Clarke and others are taken at face value - and there is no reason to believe they should not be - there is a desire for unity behind the new prime minister in the run up to the next general election.
Thursday's local and regional election results will have hammered home that message and perhaps helped persuade possible anti-Brown rebels that attempts to defeat or destabilise him would only harm Labour's longer-term prospects.
It is even beginning to look like that "stable and orderly" transition of power once talked of by Labour bosses is now underway.