The First Sea Lord and Chief of the Naval Staff has been selected by the Prime Minister as the next head of the Armed Forces, The Telegraph can reveal.

       Admiral Sir Tony Radakin will take over from General Sir Nick Carter as Chief of the Defence Staff, making him the first military chief to come from the Navy since Admiral Sir Michael Boyce in 2001.

       Sources close to General Sir Patrick Sanders, who was seen as the First Sea Lord’s biggest threat to securing the role and believed to be the Ministry of Defence’s recommendation for the position, confirmed he had not been successful in the race.

       They added that he was “relaxed” about the decision.

       Downing Street is expected on Thursday to formally announce Boris Johnson's choice of defence chief.

       It is understood that Vice-Admiral Sir Ben Key, who led the Afghanistan evacuation and is in charge of all overseas military operations, will be promoted to Admiral and replace Sir Tony as First Sea Lord.

       The contest for the new head of the Armed Forces has long been considered a two-horse race between Sir Tony, for his knowledge of the seas and Sir Patrick, owing to his deep understanding of how to integrate cyber capabilities into the Armed Forces.

       However, others in the mix to clinch the post included General Sir Mark Carleton-Smith, the former head of Britain’s special forces and a personal friend of Mr Johnson.

       Under Sir Tony, the UK has seen two new aircraft carriers brought into service. He also oversaw the deployment of one, HMS Queen Elizabeth, including escort ships and a hunter-killer submarine, to the Indo-Pacific region. As a result the Royal Navy is seen as embodying the Government’s Global Britain agenda.

       Meanwhile sources have said that the recent Aukus deal with the US and Australia over the future provision of nuclear submarine capability reflected well on the First Sea Lord.

       Earlier this year The Telegraph revealed that Sir Nick, 62, who was in his third year as Chief of the Defence Staff and was due to retire, would remain in post until the end of the year so that he could lead the transformation of the military following the Integrated Defence Review.