For one thing, delaying a byelection goes against current Labour instincts about such matters, which are haunted by the loss of Brent East to the Liberal Democrats in 2003 - a byelection loss now put down by the party to the three-month gap between the death of Labour's Paul Daisley and polling day. Modern byelections have to take place quickly, one former Labour manager argued to me before Glasgow East. Going early maximises your own control, minimises your own weaknesses, denies your opponents time, and, if you lose, it gets the bad news out of the way.
This last is a potent factor in any calculations about Glenrothes. If, in the real world, Labour is bound to lose there, then what is the advantage of delaying? In the wake of Glasgow East, nobody expects Labour to hold Glenrothes, so would it not be best - or least worst - to just take the hit?
The crucial political question about Glenrothes is whether a defeat there will trigger a challenge to Brown. There are no easy answers, but the impact of a November defeat in Glenrothes on a relaunched, reshuffled and even modestly resurgent Labour party would in my view be much more damaging to Brown than the impact of a September defeat on a Labour party fully braced for the loss and ready, in the aftermath, to stand by its leader as he attempts to turn things around.
None of this, let's be clear, does much, if anything, to address Labour's central current problem. That problem, as a former minister graphically puts it, is that the electorate now thinks of Brown in the same way as a householder who sees an unwelcome visitor through the spyhole in the front door when the bell rings. At first, the householder just refuses to answer the door. But if the same visitor simply goes on ringing the same bell, the householder will go to any lengths to get rid of him. Labour's challenge is to work out how to persuade the electorate to answer the door. That's partly about the face they see through the spyhole, but in the end it is even more about the message he brings.
Seen from now, in the middle of August 2008, Labour seems willing to allow Brown another chance to ring the bell on its behalf. In my view that is a piece of self-indulgence Labour cannot afford. Yet if I am wrong, as I may be, and the Brown strategy is to have some chance of succeeding - however modestly such success must now be defined - then Labour has to find a way of taking the electorate's punch in Glenrothes and not allowing that punch to lay it on the canvas. That way is to hold the byelection at the earliest possible, if ominous, date: September 11