By Brian Wheeler BBC News political reporter

Harold Wilson's belief that he was the victim of a secret service plot to discredit him is well documented.

Wilson believed MI5 were plotting against him

But new revelations in BBC drama documentary The Plot Against Harold Wilson, to be broadcast next Thursday, suggest the Labour prime minister was also convinced he was the target of plans to stage a military coup - and that the Royal Family backed it.

The story sounds barely credible - a sign, perhaps, that Wilson was suffering from paranoia - but it is backed up by corroborating interviews with other senior figures from the time.

The then BBC journalist Barrie Penrose has outlined some of the detail of the new evidence in an article in this week's Radio Times.

He stresses the need to bear in mind the backdrop to the alleged plots, telling the magazine: "Our establishment, from the intelligence services down to parts of Fleet Street, were paranoid about the threat of communism. So paranoid it seems, they were prepared to believe a prime minister of Britain was an active Soviet spy."

At a time of continuing Cold War tensions, industrial unrest was rife, the country had suffered power cuts and a three day working week and in 1975 the government was being warned privately that the economy faced "wholesale domestic liquidation" unless it could tame inflation.

While some on the hard left believed revolution was imminent, former military figures angry at the extent of union control were building private armies, in preparation for the coming conflict.

Fears

And it is these mercenaries, the programme says, that Wilson feared would be used to stage a coup against him - and that the British army might not come to his aid.

Industrial unrest was at its height in the early 1970s

In his book Spycatcher, Peter Wright tells of a plot to force Wilson's resignation by MI5 agents convinced he was a Communist spy. Wright's account is often dismissed as an exaggeration, but the drama documentary claims fresh evidence of plots.

The meetings with Wilson the programme is based on were secretly recorded in 1976 by journalists Barrie Penrose and Roger Courtiour, weeks after his shock departure from Number 10.

"Wilson spoke darkly of two military coups which he said had been planned to overthrow his government in the late 1960s and in the mid 1970s," Penrose writes.

"Both were said to involve high-ranking elements in the British army, eager to see the back of Labour governments.

"Both involved a member of the Royal Family - Prince Louis Mountbatten."

Lord Mountbatten would be installed as an interim prime minister following the military coup, Wilson believed.

Secret recordings

Baroness Falkender, Wilson's political secretary, also told the two journalists about her belief military coups had been planned and that she and Wilson would be arrested with the rest of the Labour cabinet, Penrose writes in the Radio Times.

Occasionally when we meet I might tell you to go to the Charing Cross Road and kick a blind man standing on the corner Harold Wilson

"Unbeknown to Wilson, Courtiour and I secretly recorded many of our meetings with him, almost always conducted at his Georgian house at 5 Lord North Street, close to the House of Commons," Penrose says.

"The cumbersome machine was smuggled into his study in a briefcase carried by Courtiour. Over a period of nine months we accumulated hours of tape recordings. Those tapes have, since then, remained untouched in the loft of my Kent home and at Courtiour's London home."

Wilson told the journalists they "should investigate the forces that are threatening democratic countries like Britain".

They were also startled to be told at their first meeting with him: "Occasionally when we meet I might tell you to go to the Charing Cross Road and kick a blind man standing on the corner. That blind man may tell you something, lead you somewhere."

The pair were never asked to go to Charing Cross Road but Wilson went on to tell them about his distrust of a group of MI5 officers, who he said were trying to smear him by planting stories in the press about him being an adulterer and a Communist spy.

In one of the secretly recorded tapes Wilson says: "I am not certain that for the last eight months when I was prime minister I knew what was happening, fully, in security."

New witnesses interviewed for the programme talk about these military coups and Mountbatten's role in them. Penrose says they confirm such plotting "wasn't in the fevered imagination of an embittered ex-PM".

Penrose concludes his Radio Times article: "You may ask, at the end of the programme, how much of it can be believed. My view now, as it was then, is that Wilson was right in his fears.... in answer to the question 'how close did we come to a military government' I can only say - closer than we'd ever be content to think."

The Plot Against Harold Wilson is on BBC Two at 2100GMT on Thursday 16 March 2006.

Send your comments on this story, using the form below.

The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.