Guardian journalist Dave Hill has said Sadiq Khan lost faith in Jeremy Corbyn during the Brexit referendum campaign.
The London Mayor revealed his decision in an article for The Guardian yesterday. He said "the Labour party must ultimately unite again" and expressed the belieft that "Owen Smith is the best person to lead that fight" at the next General Election.
Hill, a commentator for the newspaper, told talkRADIO Corbyn's lack of clarity in the referendum campaign was a key factor.
"It wasn't clear even to Labour supporters where the leader stood on that," he told Paul Ross. "That's part of the reason that Sadiq Khan has chosen to back Owen Smith.
"But I think it's also about other things. It's about know-how, it's about winning.
"He can say he's won elections with quite fierce competition, and Jeremy Corbyn doesn't know how to do that."