Friends of the suspended head of the Royal Navy have said he has been the victim of a "stitch-up" engineered to oust him. Admiral Sir Ben Key has been told to "step back from all duties" while claims he had an affair with a female officer are investigated.

Britain’s top sailor, 59, is married with three children and now faces a misconduct inquiry, the first ever to be launched against the occupant of that office. Admiral Key was due to be replaced by Royal Marine General Gwyn Jenkins in the summer but has been stopped from leaving his post early to allow the investigation to run its course. His disciplinary inquiry is reportedly already underway, with staff at Portsmouth’s Navy Command due to be interviewed over the next few days. Friends of the under-fire sailor claimed the allegations were a "stitch-up" and part of months on in-fighting at the top of the armed forces, The Times reported.

Sources told the Mail on Sunday Admiral Key clashed with other senior officers over financial cuts, including the chief of the defence staff Tony Radakin.

A Navy source told The Times: "I think he has been stitched up to get him out of the picture. He had constantly raised questions about the delays with new ships, funding for recruiting and the lack of frigates, and he was told to keep quiet. Now he can’t say a thing."

Another source said: "It is all too convenient. There was a massive bust-up over the future direction, funding and policy of the Royal Navy. It’s not a big secret the Navy is in deep trouble."

The investigation into Admiral Key will centre on whether he broke the “service test”, which does not allow sexual relationships between commanders and their subordinates.

There is no suggestion that Admiral Key’s behaviour was criminal.

The suspended naval chief has repeatedly vowed to crack down on unacceptable sexual behaviour, promising in 2022 he would expel anyone who refused "to service in accordance with the values and standards of life in the United Kingdom’s armed forces".

The Ministry of Defence told The Times: "An investigation is ongoing and it would be inappropriate to comment at this time."