Liberal Democrat London mayoral candidate Brian Paddick has accused Ken Livingstone and Metropolitan Police commissioner Sir Ian Blair of "collusion".

Paddick said that Sir Ian "could do no wrong" in the eyes of the mayor and was always being defended by him - despite some of his "questionable" actions.

He also asked why Livingstone did not chair the Metropolitan Police Authority when crime was such an important issue for Londoners.

The former Metropolitan Police deputy assistant commissioner said as the "expert" on the subject of crime, he was well-placed to hold the position of mayor.

Asked if Sir Ian and Livingstone were "thick with each other", he told BBC1's Andrew Marr Show: "Well there does seem to be a bit of collusion going on between the two.

"Whatever Ian Blair does, and some of the things are slightly questionable, in terms of whether they were the right thing to say at the right time, according to Ken Livingstone Ian Blair can do no wrong."

He added: "All our polling shows that crime is the number one issue and surely you should have the expert on crime as mayor if that is your number one concern."

And he suggested Livingstone should be chairing the Metropolitan Police Authority.

"The MPA selects the commissioner, decides the budget, decides on the priorities of the London police," said Paddick.

"The law has changed now so Ken Livingstone could do that as well. He chooses to chair transport for London rather than the metropolitan police authority but if that is the real major concern of Londoners why isn't he chairing that committee?"

Responding to the comments, a spokesperson for Ken Livingstone's campaign said: "The problem with Brian Paddick's positions on crime is that he starts from his wrong claim that the reduction in serious crime in London is only due to 'under reporting'.

"This is nonsense. Murder for example has fallen by 28 per cent in the last five years, from 222 to 160 last year, and there is no significant under reporting of murder in London - no pile of undiscovered bodies somewhere.

"Brian Paddick wants to conceal the fact that under Ken Livingstone crime has fallen for five years in a row, due to increasing police numbers, and Brian Paddick's pledge that he would reduce crime by five per cent a year is actually less than the average annual fall under Ken Livingstone in the last three years - Brian Paddick pledges a worse crime record than is being achieved."

The row came as Labour activists were warned that the race for mayor of London will be the closest since the office was created eight years ago.

The declaration came from minister for London Tessa Jowell, speaking at the party's spring conference in Birmingham.