I agree with Clare Short (interviewed on Radio Four's PM) that it is not entirely necessary for Blair to stand down as an MP purely because of his Middle East envoy role, which is not full time. It doesn't involve chairing standing talks, for example. It will probably involve just the odd trip, which Blair has managed to fit in with two other roles for years, so fitting it in with one role wouldn't have been a problem.
He just hasn't got the patience to carry on has he?
I am sure Brown will welcome it, because it means there is no chance of sulking on the back benches. It is traditional that retiring PMs (e.g Major, Heath, Churchill) stay on until at least the next election (Heath went on far longer). But Blair is no normal human being, of course. He has millions (mainly dollars) to earn.
In reply to Newbury Blogwatcher and others who have suggested that this will overstretch the LibDem by-election machine...Sedgefield and Ealing are so far apart that this hardly arises as a problem. In the main, people who are likely to travel to Sedgefield to help are not the same people who are likely to travel to Ealing to help.