Sadiq Khan has insisted he is “not at all” interested in becoming Labour leader.
The London mayor is regularly tipped as a future party chief, despite no longer being an MP.
Keir Starmer and his deputy, Angela Rayner, have said they will quit if they are fined by Durham police over the beergate scandal.
On the BBC’s Sunday Morning programme, Khan said that set him apart from Boris Johnson and Rishi Sunak, both of whom have been fined but remain in post.
Asked if he wanted to be Labour leader if Starmer resigns, he said: “No. But it is a good compare and contrast about the integrity of Keir Starmer and Angela Rayner versus Johnson and Sunak.
“The public should understand that one of these characters, Boris Johnson, presided over a culture of law-breaking.
“The other guy has the integrity to say, ‘You know what? If there is a fixed-penalty notice, I’ll quit’.”
Pressed again on whether he had ambitions to lead Labour, Khan replied: “Not at all.”
HuffPost UK revealed last month how Khan had angered several members of the shadow cabinet by setting up a commission to examine the UK’s drugs laws.
Former Labour frontbencher Lord Falconer will chair the new body, which will make recommendations on what more can be done to tackle drug-related crime.
But some senior frontbenchers, including shadow home secretary Yvette Cooper, are furious at Khan’s plans, fearing it will allow the Tories to portray Labour as soft on drugs.
“Yvette is furious about it,” a Labour source said. “People are just rolling their eyes because it definitely is not the official party line.”