By Nick Assinder
BBC News Online political correspondent
Tony Blair's extraordinary statement that, if he wins the next election, he will quit before a fourth possible term, was clearly designed to end the leadership speculation that has gripped Westminster for months.
It may or may not do that, but what it will most certainly do is spark the longest leadership campaign in recent history.
And what has long been seen as a foregone conclusion - Gordon Brown's succession - must now be simply just one of the many possible outcomes.
Gordon Brown has long been seen as Tony Blair's successor
First off, the prime minister's suggestion that he will complete a full third term before standing down must be open to question and not just because he appears to have bought his luxury retirement home.
It would be unthinkable for him to quit only a few months, let alone weeks, before a general election, landing the party with a leadership battle at a crucial point.
So it is far more likely he will stand down after a couple of years or so into the third term to give his successor time to bed down.
It may even be that, in the immediate aftermath of that general election, speculation about precisely when he will go will become so intense he has to go sooner rather than later.
So, in some ways, the prime minister's announcement has only confirmed what has already been the speculation in Westminster.
Previous suggestions he was on the verge of quitting have recently been dismissed and most had accepted he was ready to fight the next election and stand down some time during the third term.
Now we seem to have that as a set-in-stone fact.
All this means that would-be successors have been given a clear target to aim for. And they have one simple task - to see off the man still seen as most likely to succeed, Gordon Brown.
Alan Milburn is one of several possible leadership candidates
That is assuming Mr Brown does not now believe the prime minister has so damaged his chances of taking over that he considers his career options.
As the prime minister said himself: "There are lots of people who want to do the job."
His latest favourite, Alan Milburn, is certainly one, but virtually any member of the Cabinet might think they are in with a chance.
That could, then, include Foreign Secretary Jack Straw, Home Secretary David Blunkett, Commons leader Peter Hain, Education Secretary Charles Clarke, Trade Secretary Patricia Hewitt and maybe even former minister Robin Cook from the left of the party.
Equally, with three or four years before the leadership battle, there are any number of rising stars who may believe they will have made enough mark by then to pitch for the top job.
Anyone who fancies their chances will, therefore, start positioning, and quietly campaigning.
The Tories have already leapt on this to suggest the government will now spend the next four or five years distracted by the leadership contest.
Downing Street, on the other hand, has clearly calculated that there is no chance such speculation can be sustained for four or five years and will soon die down.