He has what he describes as 'new and conclusive evidence' of his long-held claim that the real Robin was Robert de Kyme, born around 1210 at Bilborough in Nottinghamshire - stepson of a direct descendant of the Earl of Huntingdon, but disinherited because of his 'wild living' and debt.
It seems unlikely that the evidence, culled from an 1864 pamphlet by J R Planche of the College of Arms, will be enough to convince professors of medieval history that Mr Lees is anything other than an eccentric enthusiast. But the author of The Quest for Robin Hood (Temple Press, 1987) has been shrugging off what he calls 'academic snobbery' for half his life. 'It's water off a duck's back,' he said in his robust Nottingham brogue.
Makers of feature films and documentaries have beaten a path to the bungalow he shares with his long- suffering wife, Margaret. 'I've had enough Robin Hood to last me a lifetime,' she said, good-naturedly. Mr Lees snorted dismissively. 'It's opened up a new life for her,' he retorted. 'Look at those vases on the mantelpiece. They're Japanese, you know. The Japanese love Robin and their tourists visit us when they're in Nottingham.'
A researcher called to consult him for the 1991 Kevin Costner film, Robin Hood: Prince of Thieves. 'They would have made changes to the script, but they were in a bit of a hurry. There was another Robin Hood film being made at the same time. They rang and offered me a walk-on part,' he added, with an ironic glance at his zimmer frame.
'CBS wanted me to go to Sherwood Forest to film their documentary. I said I'd rather do it in the back garden. There are plenty of trees out there. After it was shown, I had a letter from a bloke in Ohio who said he'd seen the Kevin Costner film and hadn't been fooled. He knew when he saw me that this was the real Sherwood Forest. What he didn't know was that I was standing next to our ornamental cherry tree when they filmed it.'
It was to satisfy the curiosity of Americans that Mr Lees began his quest for Robin back in the mid- 1950s. He was running his own business as a blouse manufacturer during the week and working as a square-dance caller on Saturday nights. Nottingham was a magnet for US airmen based to the east of the city. Weaned on Errol Flynn, they had one burning question when the music stopped: 'This guy, Robin Hood, was he real?'
Before long Mr Lees was organising trips 14 miles up the road to what's left of Sherwood Forest. 'I'd book them into guesthouses and hotels on the Saturday night and have a bus ready on Sunday morning. Afterwards, they'd come back for tea at Nottingham Castle and meet the Sheriff in his chain of office.'
Appreciative as the Americans were, their guide felt uneasy. 'I realised how little I knew about Robin. Rather than tell lies, I started to research the subject.'
So began a 40-year trawl through ancient manuscripts. He travelled all over the country, taking in the British Library and the Bodleian at Oxford. At the University library in Cambridge one day, he was approached by a kindly don. 'He asked me what I was after and I told him: Robin Hood. It's been done, he said. Not to my satisfaction, I replied. He found me some rare manuscripts. Then he asked me what I was doing for lunch and took me to Clare College. I sat at the high table with all those dons. They didn't have a clue who I was, but they were very nice to me.'
Although Mr Lees left school at 14, what he lacked in academic qualifications he more than made up for with dogged persistence. (This is a man who, coincidentally, is set to enter the Guinness Book of Records as the world's longest-serving 'boy' scout.)
His search for Robin Hood was exhaustive and exhausting. Initially, he discovered what many academics could have told him: that the myth had taken over the man. References to Robin were all over the place, says Mr Lees, but mostly he was over the border in Yorkshire, born in Wakefield and living in Barnsdale not Sherwood Forest. As a Nottingham loyalist, this was difficult for Mr Lees to stomach. 'It was partly local pride, I suppose. I discovered that Nottingham is mentioned 21 times in the ballads and Wakefield only once. I went to Barnsdale and it took more than two hours in the car. It's a distance of more than two marathons. How could Robin have got there and back in a day?'
He says this with the air of one convinced he is right. Academics are not so sure. Sir James Holt, a fellow of Fitzwilliam College, Cambridge, has long derided what he sees as Mr Lees's over-reliance on the works of Dr William Stewkley, an 18th-century historian. Michael Jones, a professor of medieval history at Nottingham University, believes that Robin was not one person. 'There are a number of characters from different periods who incorporate his features,' says Professor Jones. 'They have been brought together to create a legendary figure.'
Mr Lees seems remarkably untroubled by this scepticism. 'Just because they've got letters after their names, they'll believe them and not me,' he says. 'But the pamphlet from the College of Arms has a family tree of the de Kymes. It proves, to my satisfaction, that Stewkley was correct.' He will go to his grave contented, convinced that, unlike the Sheriff of Nottingham, he has finally got his man.