The chairman of the Metropolitan Police Authority has a criminal conviction for carrying an offensive weapon.
Len Duvall, who was appointed by Ken Livingstone, pleaded guilty to carrying a stave which was found after he was stopped and searched by police. He was fined by Woolwich magistrates.
Mr Duvall, who is also a Labour candidate for the London Assembly, told the Standard: "It was many years ago and it's something I terribly regret and have had time to reflect on. There was a lot of trouble going on [in Woolwich] at the time and I thought I needed to defend myself."
During the mayoral campaign, Mr Livingstone has criticised his main opponent, Boris Johnson, for promisingto chair the MPA despite his role in the so-called "Darius Guppy affair".
In a phone conversation in 1990, Mr Johnson promised to get his friend Guppy, who was convicted of fraud, the address of a journalist so Guppy could have him beaten up. Johnson did not supply the address and the journalist was not harmed.
Last month Mr Livingstone issued a statement saying: "The issue David Cameron must address is how he can endorse as candidate for Mayor of London, who wishes to chair the MPA, someone - Boris Johnson - who agreed to supply an address to a fraudster so a journalist could be beaten up." One police source said: "We all thought it was incredible when we heard that. Here was Livingstone saying Boris Johnson was unfit to chair the MPA because of his involvement in a crime that never happened while his own MPA chair has an actual conviction for a weapons offence."
A spokesman for the Johnson campaign said: "Perhaps Ken Livingstone should have paid more attention to those close to him rather than always taking a pop at Boris. Those who work in glass empires should not be so quick to throw stones."
Mr Duvall's conviction dates back to 1979. He said today: "It was declared to the MPA before I became chair and senior police officers know about it." Mr Livingstone is also understood to have known about the conviction.
