Boris Johnson lacks the skills necessary to be a prime minister, the chairman of the Conservative Party Grant Shapps has said.
"Boris is a great mayor, it takes a different set of skills to be in office as a minister or indeed the prime minister," he said.
Shapps' rebuke to the Tory mayor of London comes after a summer of speculation that Boris is plotting to return to the House of Commons in order to run for the leadership of the party.
Speaking on BBC Radio 5 Live's Pienaar's Politics on Sunday, the newly appointed party chair said while Boris knew how to spend money as mayor of London it did not mean he had what it took to take unpopular decisions.
"When you're in government, when you're a minister or prime minister, you have to raise the money as well [as spend it]," he said.
"You end up naturally having to make difficult decisions when you're in government which you don't have to make when you are in a position of spending."
Shapps also dismissed mutterings in Westminster that Tory backbenchers were unhappy with Cameron's leadership of the party who he said was a "very good, capable, excellent, prime minister".
"In every single government ever there's always going to be some people who say 'we are not happy'," he said.
"Ask anybody who knows anything about the way things actually operate at Westminster, there is no great groundswell."
It will not be lost on many that Shapps also pointed out that he knew what it was like to be in government, as he had served as housing minister before being appointed party chair in the recent reshuffle.
When asked recently whether he would challenge Boris for the party leadership in the future, Shapps cheekily responded simply: "Naughty".