Blairites hate Brownites. Some Blairites pretend to like Brown because they want jobs in his next government (the one he'll have without the need to win a general election). Some Blairites will just keep their mouths shut. The party looks like it might rip apart.
Then the public decide that they like Cameron more than Brown and Labour people of all shades get worried. They all start to back Brown to try and brow-beat Cameron down. The party suddenly becomes very united and all and sundry say Brown will win by default. Hence Blears saying that Blair will back Brown today.
So what happens now? An unchallenged Brown leadership? No. When Labour feel they've been ghastly to Cameron enough and nearer the time of Blair's departure, all these people who have been nice to Brown will suddenly turn again.
Expect a contest between Brown, Reid, Johnson and McDonnell.