Jon Cruddas's decision to throw his weight behind Ken Livingstone gives the former London mayor's campaign exactly the sort of momentum it needs. The Labour backbencher brings with him a small army of activists who will provide much-needed improvement works to the Livingstone machine.

I was one of those who hoped that Cruddas, an exceptional campaigner and an unusually thoughtful politician, might launch his own bid. But, as in the case of the Labour leadership, he has plainly concluded that the job is not for him.

With just three days to go until nominations close, Livingstone's hegemonic grip on London Labour shows no sign of being broken. Oona King, the only other candidate to have entered the race, brings a rare warmth and humanity to her politics but her campaign has so far failed to impress. She has yet to articulate exactly why she, rather than Livingstone, is best placed to run London.

The known unknown is how Londoners will respond to Labour presenting them with a candidate they have previously rejected. By 2012, however, with the incumbency factor likely to deter many of Boris Johnson's casual supporters, a return to Ken may seem an attractive proposition.

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