London Mayor Boris Johnson "desperately wants to be prime minister", according to Downing Street's former spin doctor Andy Coulson.
Mr Coulson went on: "If proof were needed that our PM is a man untroubled by self doubt, it came in his next sentence - 'so I think he'll be a bloody brilliant candidate for us'.
"Stabbing David, or anyone else for that matter, in the back would be distinctly off brand - just not very Boris. He would much prefer to see David fail miserably in the election and ride in on his bike to save party and country."
More top news
The mother of a missing RAF serviceman has hired a private investigator to help search for her son after raising thousands of pounds.
Dozens of potential suspects have been identified in connection with historical child sexual abuse allegations in football, police say.
Kirk Douglas, star of film classic Spartacus and one of Hollywood's last surviving Golden Age actors, has turned 100.