Last updated at 17:45 14 April 2008

Foiled: Tory prime minister Alec Douglas-Home revealed the bizarre kidnap plot from 1964 to Lord Hailsham during a shoot in Scotland

They intended to send shockwaves through the British establishment by kidnapping a serving prime minister.

But instead, a group of bungling students were scuppered by the most cliched university vice of all - beer.

The party of left-wing radicals had targeted Tory prime minister Alec Douglas-Home after tailing his car from a conference to the house where he was staying.

Astonishingly, his body guard was using separate accommodation and when the plotters knocked on the door, they were greeted by a bemused premier.

Faced with a determined group of militants, the resourceful prime minister decided that there was only one option.

Perhaps unsurprisingly, the liquid refreshment did the trick and defused any of the group's lingering desire to kidnap their genial host, along with assurances they would guarantee his party a landslide victory if they went through with their plan.

The extraordinary incident emerged for the first time in the diaries of former Lord Chancellor, Lord Hailsham.

In an entry dated January 9, 1977, the peer notes down how Sir Alec described the bizarre episode, which took place in 1964, to a shooting party at Birkhill, in Scotland.

He wrote: "An odd story of the 1964 election never published.

"Alec (then Prime Minister) was staying with John and Priscilla Tweedsmuir, who had no room for Alec's private bodyguard.

"He went to the nearest town (Aberdeen?) and John and Priscilla left Alec for a time alone in the house. Knock at the door. Door answered by PM in person.

"Deputation of Left-wing students from Aberdeen University. Said they were going to kidnap Alec.

"He, 'I suppose you realise if you do, the Conservatives will win the election by 200 or 300.'

"He asked and received permission to pack a few things and was given 10 minutes' grace.

"After that they were offered and accepted beer. John and Priscilla returned and the kidnap project abandoned.

"The bodyguard swore Alec to secrecy as his job would have been in peril."

Sir Alec first ran into the Aberdeen University students at the Scottish Unionist conference, where they demanded a forfeit for charity in return for not kidnapping him.

Assuming it was a joke, the prime minister played along and gave them £1.

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Revelation: Lord Hailsham wrote about the kidnap plot in his diaries, which have only just be declassified. The peer died in 2001

But events took a more sinister turn after the group tailed his car to Potterton House, where he was staying with John Tweedsmuir, the son of The 39 Steps author, John Buchan, and his wife Priscilla .

The plotters had intended to stage an accident, block in his car and then drag the PM to a house in Aberdeen.

But they backed out and instead decided to follow him to the house where a group were able to walk straight up to the door.

The previously unpublished papers had been written in shorthand which had to be translated by experts at GCHQ.

Lord Hailsham, who served as Lord Chancellor during the Thatcher and Heath governments had asked that his diaries were not released until after his death.

He died in 2001. The material was passed on to the University of Cambridge's Churchill Archives Centre and is now being published online by the Margaret Thatcher Foundation.

Chris Collins, editor of MargaretThatcher.org, said: "The kidnap prank was one of the worst breaches of a prime minister's personal security in the 20th century, at least that we know of.

"If Home's assailants had been darker in purpose he would have died that night."

The diaries span 1970-74, the years of Edward Heath's premiership.