By Dominic Casciani
BBC News at the National Archives
Benn: Officials worried about his brand of socialism
Political historians believe one of the principle reasons for the defeat of the Labour Party in the 1970s was the tensions between its different wings, the left largely led by Tony Benn.
Now Cabinet papers released by the National Archives provide inside detail of just how bad the relationship had become between Prime Minister Harold Wilson, his officials and Mr Benn within months of Labour taking power in 1974.
Mr Benn, who retired from the House of Commons in 2001, has documented the period extensively in his diaries.
But the Downing Street documents reveal how much some officials opposed Mr Benn's radical agenda.
Returning to government as industry secretary after Labour's narrow win in March 1974, Mr Benn soon recorded his relationship with Wilson had hit "absolutely rock bottom".
The two men clashed fundamentally on key policy areas, including Labour's relationship with the unions once in government.
Mr Benn believed in increasing "workers' control" of industry and pushed this policy as soon as he was in office.
The response from his enemies was ferocious - one political cartoon in the Sunday Express depicted Mr Benn as an undertaker burying British industry.
Senior official Sir Robert Armstrong, later to become Cabinet Secretary under Lady Thatcher, alerted Mr Wilson that Mr Benn was nevertheless planning to make a speech on this policy in early May.
The draft seen by Sir Robert was full of language considered Marxist by Benn's critics: it described strike action as an historical "struggle for the industrial franchise" which would see a "real transfer of power.
"Plans submitted by Britain's leading companies will have to be developed in conjunction with the workpeople," proposed Mr Benn.
Key to this future was following through on Labour's commitment to nationalisation - Clause Four of the party's constitution which was later dropped by Tony Blair.
In a memo Sir Robert told Harold Wilson the speech would be politically disastrous.
"This is a good deal toned down from an earlier version...but it is still heady stuff and some of it is likely to send special shivers down industrial spines," he said.
Joe Haines, Mr Wilson's influential press secretary, agreed.
Harold Wilson: Benn admitted their relationship collapsed
"Tony's speech will cause uproar without advancing his cause," he warned.
The prime minister decided to order the Cabinet minister to rewrite the speech. In his diaries, Mr Benn briefly records his row with officials over the speech - but not Wilson's furious letter.
Mr Wilson said: "I don't think you can make a speech like this...it goes a long way beyond anything that we are committed to as a Cabinet or a government.
"You have no authority to say 'the government accepts that commitment' [to Clause Four].
"None of us has had an opportunity of thinking about, let alone discussing your ideas.
BENN AND WILSON
My relations with Harold are absolutely rock bottom - I will have to consider how to improve them, he really does think that my public statements and so on are destroying the Labour Party
Tony Benn's diary, 19 May 1974
"As it is, the way you put it will simply be grist to the mill for those who say we are controlled by the unions ... [it will] undermine at a stroke all that some of us have been doing to try to rebuild a measure of confidence in industry."
Shortly before the planned speech, Mr Benn's office sent a third version of the text back to Downing Street, with key sections red-inked out.
Read by Sir Robert Armstrong again, the top civil servant thought it was now just about passable.
"The eyes still flash but the feet do not tingle quite so heavily," he told the prime minister.
Mr Wilson appeared satisfied and allowed the matter to drop. But his rebellious Cabinet minister was not entirely prepared to toe the line.
Within weeks he had sparked more fury in Downing Street when he abstained on a minor technical vote in the Commons, something colleagues took as a signal of his dogged refusal to do as he was told.