David Cameron said he would give London Mayor Boris Johnson "a warm welcome" if he decides to return to Parliament.
The Prime Minister told ITV News' deputy political editor Chris Ship: "I think he's got a huge contribution to make.
"Whenever Boris wants to, he'll get a warm welcome from me".
Boris Johnson reminded Tory conference delegates of his prediction that last year's London Olympics and Paralympics would spur a baby boom.
He told the Conservative Party conference: "I prophesied that the athletes had moved the people of this country to such paroxysms of excitement on the sofas of Britain that they had not only inspired a generation, but probably helped to create one as well."
"Like all my predictions and promises, I have delivered, in that GLA demographics say live births in London will be 136,942, which is more than in any year since 1966 when England won the World Cup."
Mayor of London Boris Johnson has observed that in France they can be both a mayor and Prime Minister at the same time.
A very good idea, he said:
Boris has just encapsulated the Tory problem - he asks who in the audience is from Surrey, Buckinghamshire or Sussex? Lots of cheers.
Who is from Oldham or Darlington? Silence.
London Mayor Boris Johnson highlighted celebrity chef Jamie Oliver's comments about the work ethic of British young people during his conference speech.
Mr Oliver praised European immigrants in August, saying they are much "tougher" workers than the "wet behind the ears" young Brits.
Mr Johnson asked delegates, "What if he has half a point? Or a quarter of a point?"
He said if that indeed was the case, "don't we need Iain Duncan Smith to get on reforming the welfare system and ensuring you're always better off in work than out of it?"
"And if it's to do with education ... then don't we need Michael Gove to get on with his heroic work of restoring rigour and realism to the classroom?"
Boris Johnson asked the Chancellor George Osborne "to look at the baleful effects of stamp duty" in London and elsewhere during his conference speech.
The Mayor of London told the Conservative Party conference: "It's called stamp duty for a reason, because it's stamping on the fingers of those who are trying to climb the property ladder.
Boris Johnson said the Conservatives have "to recognise that the sheer global charisma of London is putting pressure on Londoners."
Addressing delegates at the Conservative Party conference, the London Mayor highlighted that average house prices are now six times average earnings in the capital.
"The pressure is really growing and it's intensifying," he added.
The Prime Minister has hinted that talks are under way over a return to Parliament for Boris Johnson.
David Cameron said he had had discussions about a possible return with the London Mayor, although he stressed that a decision had not yet been taken.
Asked how likely a return was, Mr Cameron said:
"That's up to Boris. I've had this conversation with Boris and my message to him is 'You're a brilliant Mayor of London, you've done a great job, you've got a lot more to give to public life, and it would be great to have you back in the House of Commons at some stage, contributing to public life'. But that's up to him, but I'll certainly be giving him a warm welcome."
Asked if Mr Cameron could see his former Eton schoolmate make a comeback as a Member of Parliament at the next election, he replied:
"Absolutely - but that's a matter for him. I think he needs to think about - it's his plan. All I know that he's a massive asset to the country, a massive asset to the Conservative Party. We could make a very strong team together, we do today."
Also quizzed on whether there was a potential job for Mr Johnson within the party, Mr Cameron said:
"Obviously, this is all dependent on what Boris wants to do - whether he wants another term, whether he wants to become an MP.I think he's got an enormous amount go give to public life, and I don't think he's given up on that idea either. So I think we're quite well aligned if I can put it that way."