Ken Livingstone
Oh dear: Ken Livingstone has made some choice comments (Reuters)

Labour's London mayoral candidate Ken Livingstone seems to find his feet pretty tasty.

He has a book's-worth of foot-in-mouth comments, many of which have caused outrage.

In his latest outburst, he said in a Metro interview that a gay banker would not go to Dubai because he would "get his penis cut off".

It followed comments Livingstone made in a New Statesman interview that the Conservative Party was "riddled" with homosexuality.

Livingstone was making the point that in the 1980s and 90s there were many closeted Tory MPs who hypocritically voted against gay people to conceal their sexuality.

It was his choice of the word "riddled", usually used to describe something infected with disease, that caused uproar.

A joke in 2011 comparing the battle for London's mayorship between himself and Conservative incumbent Boris Johnson to that of Churchill and Hitler also caused a stir.

"It's a simple choice between good and evil. I don't think it has been so clear since the great struggle between Churchill and Hitler," Livingstone said.

He followed up with a jest that could alienate parts of the Christian voting community.

"Those who don't vote for me will be weighed in the balance come Judgment Day. The Archangel Gabriel will say, 'You didn't vote for Ken Livingstone in 2012. Oh dear, burn for ever. Your skin flayed for all eternity'," he said.

The Hitler comment was not the first time Livingstone, who was mayor of London from 2000 to 2008 before being ousted by Johnson, invoked the Nazis to make a point. In 2005 he was suspended from office for a month after likening a Jewish journalist to a Nazi concentration camp guard.

Another anti-Semitism row blew up when he told two Jewish businessmen with investments in Stratford to "go back to Iran and try their luck with the ayatollah" after a row about London 2012 developments worth £4bn, in which they held a 50 percent stake.

David and Simon Reuben, the targets of the comments, are of Iraqi-Jewish descent and born in India.

Work on Olympic sites stalled for six months because of disagreements involving the Reubens but after an investigation by a Greater London Authority standards committee, Livingstone was cleared of charges of anti-Semitism.

One dig at Johnson's chief of staff, Eddie Lister, likened him to a Bosnian-Serb mass murderer and war criminal. Livingstone called him "the Ratko Mladic of local government" in 2011.

And the former mayor has even managed to upset the US ambassador, Robert Tuttle, in 2006. Tuttle refused to pay London's congestion charge by claiming he was exempt from it under the Vienna Convention, which allows diplomats certain rights and privileges.

"It would actually be quite nice if the American ambassador in Britain could pay the charge that everybody else is paying and not actually try and skive out of it like some chiselling little crook," Livingstone said.

In 2004 he said, rather uncontroversially, that he hoped democracy would be installed in Saudi Arabia, but it was his call for the deaths of the Saudi royal family that landed him in hot water.

"I just long for the day I wake up and find that the Saudi royal family are swinging from lamp-posts and they've got a proper government that represents the people of Saudi Arabia," he said.

With a back catalogue of less-than-diplomatic comments, the question remains whether these will hinder his chances of re-election in a race that is currently neck-and-neck.

Before Johnson starts smirking at Livingstone's latest foot-in-mouth moment, he should remember he has made more than enough gaffes of his own, not least referring to foreign black people as "flag-waving piccaninnies" with "watermelon smiles".