Jo Johnson will be appointed as Cabinet Office minister later today, Downing Street confirmed. His core remit will be to head up the Downing Street policy unit which until now has been presided over by a civil servant.
Sources suggest he will be expected to sharpen Tory strategy ahead of the next election and try and claw back support from party malcontents.
Later today Mr Cameron is expected to announce a new Conservative parliamentary advisory board. They will include Jesse Norman, who led the rebellion over House of Lords reform, Mr Cameron's former press secretary George Eustice, Peter Lilley, who was social security secretary under John Major, former schools minister Nick Gibb, Jane Ellison and Paul Uppal.
But it is the appointment of the brother of the London Mayor that is likely to elicit surprise, as well as criticism from some quarters. The MP for Orpington remains a largely unknown entity inside senior government, having only entered parliament in 2010.
Like the Prime Minister, he attended Eton College before Oxford University and was even a member of the notorious Bullingdon club. A former Financial Times journalist with degrees from two continental universities, Mr Johnson was widely tipped to forge a career inside the Foreign Office.
Last night a Conservative source told The Daily Telegraph that the appointments were indicative of a "more Thatcher-style" policy unit designed to "strengthen the connective tissue between Downing Street and the Parliamentary Party". He added: "Jo Johnson will be a great asset in helping the Prime Minister drive Conservative policy priorities throughout Government."
Downing Street confirmed the appointments yesterday but declined to comment further.