And Professor Stafford said: "Hess thought he could interpret the Fuhrer's wishes, even if Hitler didn't know them himself.
His peace mission to Scotland came at the bleakest point of Britain's war with Germany.
Pearl Harbour had yet to shatter American neutrality, and Adolf Hitler had not blundered into Russia.
Despite victory at the Battle of Britain, most people feared an imminent Nazi invasion.
So what prompted Hess, Hitler's loyal friend, to try to negotiate peace? Did he act alone or on Hitler's authority? And why did he fly to meet the Duke of Hamilton, who had no obvious political clout?
Conspiracy theorists have found as much mileage in the story as the Kennedy assassination, or Hitler's own fate.
And yet these theories are merely yarns, according to Edinburgh University's David Stafford.
The professor is editing a book of essays about the Hess mission entitled "Flight from Reality".
'Absolute twaddle'
"The truth is actually as fascinating as the conspiracy theories," says Professor Stafford.
These theories include suggestions that MI5 knew Hess was coming and was in on the plot, that he was murdered and a double substituted, or that he 'conveniently' died in a plane crash in 1942.
"It's all absolute twaddle," says Roy Nesbit, a Royal Air Force pilot during World War Two and a researcher at the Public Records Office.
He, too has written a book - "The Flight of Rudolph Hess - Myths and Reality".
"Hess was misguided enough to believe that the Duke of Hamilton was involved in a Peace Party, which he wasn't," he said.
And Professor Stafford said: "Hess thought he could interpret the Fuhrer's wishes, even if Hitler didn't know them himself.
"He was convinced that Hitler shared his view, that it might still be possible to find a rapprochement with Britain, and that the deal which had slipped though their fingers at Munich could be rescued."
Turning to the theory that MI5 knew about the mission and Hess was expected, Professor Stafford admitted that military intelligence did intercept a letter Hess wrote to Hamilton suggesting peace talks.
Hamilton never replied to the letter because he never received it - MI5 saw to that.
Once Hess arrived, Stafford says, there was a campaign of disinformation by the military and the Foreign Office, which was intended to alert Stalin to the prospect that Hitler might be about to make peace with Britain.
Propaganda coup
That plan apparently succeeded and Professor Stafford believes that the Soviet archives are the source of the theory that Hess was being taken seriously by the British Government.
"In reality, Winston Churchill wanted to use Hess quite differently," Professor Stafford insists.
"He wanted to make a propaganda coup out of the capture, parading Hess as a sign that the Nazis were divided amongst themselves."
But documents show that the prime minister lost the cabinet argument to ministers who were in favour of the disinformation campaign.
But the question remains - what did prompt this flight, which must count amongst the most eccentric diplomatic missions in history?
As well as the notion that Hess was losing his grip on reality in his desire to sue for peace, there is another important factor.
"My father was the first aviator to fly over Everest, " says Hamilton's son, the Conservative politician, Lord James Douglas-Hamilton.
Hess was an aviator too, and in the 1930s flyers were public heroes.
Lord James said that both men attended the Olympic Games, although they never met.
"It is almost as if he was trying to do a Munich in reverse, flying to Britain as Chamberlain had flown to Germany," said Professor Stafford.
Hess thought hw would find a sympathetic ear with the Duke, but he was disappointed.
Frequent visits
Rounded up by the Home Guard, he eventually found himself on trial at Nuremberg as a war criminal and ended his life in Spandau jail in Berlin.
Professor Stafford also insists that the theories of Hess's double can be dismissed.
He says fellow Nazis recognised Hess at Nuremberg, and his son visited him frequently in jail.
"His son has never said it wasn't his father," insists Professor Stafford. "
"But what really did happen to Hess is as gripping as a story - and it is the truth."