The resignation of David Miliband is a hammer blow to Labour’s chances of re election. There will be whoops of joy from the left, champagne flowing in the trade union bunkers and horror and despair amongst the Blairites.

If anyone is deluded enough to be believe that this will heal the gaping fissure that divides Labour they deserve to be taken into a place of safety. David Miliband represented the electable wing of his party. He no longer is the fantasy figure that will pick up the pieces after the walking catastrophe that his brother represents. It means that Red Ed has returned. And if the Tories have any sense they will milk this for all its worth.

There will now be a period of trauma for the Blairites. Who on earth can be the standard bearer of common sense and electability who is still in the Commons? At the moment nobody springs to mind. Andy Burnham? A busted flush and far too nice. Think Andrex puppy. And the Mid Staffs horror story happened on his watch. Alan Johnson? To old and too lazy. So who is in the running?

I wouldn’t be at all surprised if we see a lot more of Chuka Umunna on our television screens in the next few months. He is close to Ed as he was once his PPS, he is untainted by Brown and is fiercely ambitious. I am not suggesting for one moment that he would replace Miliband before the next election. Even if the party wanted it (which they don’t) the Byzantine election process would stoke the flames of the slow burning civil war that has riven Labour since the fall of Brown.

There must come a time when Miliband must realise that his economic strategy is an electoral disaster and that Ed Balls is pure poison. The the opinion polls published in the Guardian yesterday must have made terrifying reading. The public trust Cameron and Osborne to steer the economy through these troubled times more than the two Eds. Sacking Balls and replacing him with Umunna might just turn the tide. The trouble is the policy would have to change and be Osborne lite. The left would go mad. Balls would mobilise the unions and once again there would be the omnipresent fighting for the soul of the party.

It’s what Ed needs to do. But I would be amazed if he did.

If you think that Cameron has problems on the back benches from his right wing, Miliband’s lefties are just beginning to flex their muscles. That vote on benefits last week saw over forty MPs defy a three line whip. This is just the start. These are the opening shots of a genuine lurch to the left. Lynton Crosby take note.

But the South Sheilds by election is a potential disaster for Labour. The Tories who trail them by about eleven thousand are going to be wiped out. Not because of the unpopularity of the Coalition but because of tactical voting. Remember the BNP racked up nearly two and a half thousand votes in 2010. If Farage has the courage to stand there could be a major upset. In Eastleigh the kippers took votes from Labour too and Farage has made it quite clear that he is now gunning for Labour.

This could be very interesting.

Oh, and prepare for Mandelson to go on manoeuvres again. He and Blair will not stand by and allow their beloved project to end up as a cracked and forgotten monument in a graveyard of expectations.

The next few weeks are going to rather good fun.