David Cameron has said he would welcome Boris Johnson back as a Conservative MP, should the Mayor of London decide to stand in 2015.
Questioned on whether the Mayor should stand for the Commons, despite not finishing his term as Mayor until 2016, the Prime Minister told Radio 4's Today programme that it would be "great to have Boris back".
"I think he's got an enormous amount to give to public life, and a lot more to give, and I think that on that, Boris and I are quite well aligned," he told the programme.
Whether he felt able to devote time to both the Commons and the Mayoralty was "up to him", the Prime Minister said.
In a fringe event at the Conservative party conference in Manchester last night, Johnson stressed his loyalty to the Prime Minister.
"Ukip if you want to," he said. "David Cameron's not for kipping. Unless obviously he is at his sister-in-law's wedding."
The mayor's profile at this year's conference is much lower than it was last year, in the spotlight of "Olympomania" - when he was mobbed by journalists as he arrived in Birmingham.