Coe along with other British athletes, chose to compete in the Soviet Union, despite calls for a boycott over its invasion of Afghanistan the previous year during the height of the Cold War.

He went on to claim gold in the 1500 metres, beating fierce rival and fellow Englishman Steve Ovett in one of the most famous races in history.

But new disclosures released today by the National Archives under the 30-year rule of the Official Secrets Act, show Coe and his fellow British athletes were directly contradicting Conservative Government policy by competing in Moscow.

In a series of four letters to the British Olympic Association (BOA) Margaret Thatcher warned it would be "against British interests and wrong" for them to compete and urges the boycotting of the Games.

In one letter to Sir Denis Follows, the then chairman of the BOA, the Prime Minister said that attending the event would not be in British interests.

She said: "The Games will serve the propaganda needs of the Soviet Government.

"There is no effective palliative, such as cutting out the ceremonies.

"I remain firmly convinced that it is neither in our national interest nor in the wider Western interest for Britain to take part in Games in Moscow.

"As a sporting event, the Games cannot now satisfy the aspirations of our sportsmen and women.

"British attendance in Moscow can only serve to frustrate the interests of Britain."

In another letter to Kenneth Short of the Amateur Boxing Association, she wrote: "I have advised British sportsmen and women and their sporting federations that it would be against British interests and wrong for them to compete in Moscow."

Many countries, including the United States and West Germany, boycotted the Games after the Soviet 40th army marched into Afghanistan on Christmas Eve 1979 in support of the pro-Soviet regime.

Thatcher wrote to Sir Denis: "Without the Americans and West Germans and the other sporting countries who have also decided to stay away, the Games will not be worthy of the name Olympics, and medals won at Moscow will be of inferior worth and the ceremonies a charade."

One official at the BOA admitted he was "upset" by its "cavalier attitude towards the letters from the Prime Minister", which were "never properly discussed in committee".

Douglas Hurd, then a Junior Minister in the Foreign Office, wanted to discredit the BOA by highlighting the fact that it had "started writing to county councils and trades union bodies of known left-wing persuasion in an effort to raise more money", so it could send more officials and sportsmen to the Games.

He told a fellow Minister: "It would be worth encouraging press interest in the fundraising contacts with left-wing groups which he reports."

But the British Government was powerless to stop British athletes competing if they so wished and the country went onto maintain its record of being one of only 14 countries to compete at every Games.

The team won a total of 21 medals, including five gold.

Besides Coe's victory in the 1500m, Ovett won the 800m, Allan Wells the 100m, Daley Thompson (pictured) the decathlon and Duncan Goodhew the 100m breaststroke.

Thatcher also wrote to the then Australian Prime Minister Malcolm Fraser, speaking of her "regret" at the BOA's decision not to boycott the Games, while memos sent between the Department of Trade and the Prime Minister's Private Secretary even discussed banning a request by the Russian airline Aeroflot to put on an extra 18 charter flights for spectators.

The Government had also urged the International Olympic Committee to switch locations from the Soviet Union but it was decided that the event should remain in Moscow.

Memos from the British Ambassador in Moscow shed light on the atmosphere in the city in the run-up to and during the Olympics.

They detail a huge upsurge in the number of police in the city and their efforts to round up dissidents.

Coe, who ironically later represented the Conservatives as an MP for five years before becoming the chairman of London 2012, never regretted his decision to defy Thatcher.

"It did cross my mind not to go," he told me once.

"As history has shown, I think I was right and they got it wrong."

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