The Mayor of London has some vital questions to answer

Whatever else, the 40th birthday party of the sister of Ken Livingstone's partner is no longer a purely private matter for family and friends. The Metropolitan Police are to investigate allegations about Mr Livingstone's behaviour, and in particular a supposed drunken tussle between the London mayor and a friend of his partner, Robin Hedges, who fell 15 feet into a stairwell.

Mr Livingstone strenuously denies the allegations and has accused the London Evening Standard, which broke the story, of being politically motivated. And it is Mr Livingstone's rebuttal, made with due solemnity to the Greater London Assembly, that is now the focus of attention. Parts of his account have been firmly contradicted by Mr Hedges and others. Assembly members are especially perturbed to learn that Mr Hedges says he was pressured by Mr Livingstone and his partner into making a statement to the effect that it had all been an accident.

These are grave allegations. The Greater London Assembly will need a good deal of convincing before deciding that Mr Livingstone has not been trying to spin his way out of trouble. In extremis, they have the power to refer him to an obscure body named the Standards Board for England that can suspend him from office.

It all comes at a difficult time for the Mayor. Londoners, struggling to see any improvements to their city under Mr Livingstone, have begun to realise the implications of his ill-thought out plans for congestion-charging. They are also unhappy with his arbitrary decision to change the timing of traffic lights at busy junctions, which has exacerbated traffic chaos and smacks of political opportunism. His proposal to pay such handsome salaries to his staff has also raised eyebrows.

Sadly, these stories confirm a certain capriciousness in the Mayor's character that has been glimpsed before in his political career. As the deadline approaches for Mr Livingstone to reapply for membership of the Labour Party, and as Labour turns to choose its candidate for the mayorship, it is looking increasingly like the party might be better off next time without Citizen Ken.