I first encountered John Slater in his cave on an exquisite late summer day. He is a big, athletic-looking man with an Old Testament white beard, but as serene as a Buddhist guru.
Seal pups were cavorting off the isolated Wester Ross beach, with Skye a dark, mountainous smudge wreathed in clouds on the horizon. It would have been idyllic but for the Parisian photographers climbing the roof of the cave. Even they lent a certain whimsical charm to the scene, using smoke-bombs and lighting to make the cave look even more dramatic.
Our inspirational quarry was a man who indeed marched to a different drummer - or rather, walked, and in his brightly striped pyjamas. In his youth, John was a Royal Marine commando. ''There came a time,'' he said, ''when I lost interest in learning how to kill a man using only my thumbs.'' He went to live as a social work care assistant among down-and-outs in London, so he could feel he was contributing more directly to the welfare of humanity and learn more about himself. (Both these goals are not untypical eccentric pre-occupations.) His first public eccentric act to achieve some notice was volunteering to live for six months in Regent's Park Zoo as a human exhibit, to raise funds for the giant panda's conservation. The zoo, he said, foolishly and shortsightedly declined his voluntary gesture.
After this, his career became chequered, including periods of working as a musician, lorry driver, salesman, jingle composer, waiter, painter-decorator, driftwood furniture maker, tour guide, and speaker. Such a history is reminiscent of Ferdinand Waldo Demara, the Great Imposter, except that John has always been true to himself, a genuine ''straight arrow''. John's next big adventure, again intended as a charity fund-raiser, was a walk along the very edge of Scotland's coastline - 3000 miles, he says, if you tread the very brims of every single bay and inlet and peninsula. John, of course, did tread them all, with the relish of a true explorer.
On day two he tumbled into a crevasse and his wallet fell into the sea. Undeterred, he pressed on, trusting in the hospitality of crofters and fishermen. The trek took four months, gained publicity but little cash. To his thinking, this meant his next outing had to be more spectacular. ''I know!'' he told his girlfriend. ''I'll walk from Land's End to John O'Groats.''
''Done to death,'' his girlfriend retorted.
''I'll do it barefooted, then.'' His girlfriend sighed. ''And in my pyjamas!'' She lifted an eyebrow. Taking that as her blessing, he did 600 miles of barefoot training to toughen the soles of his feet. After that he got into a pair of white pyjamas with red and green stripes and hitchhiked down to the starting point, at the tip of Cornwall. He was accompanied by Tiny, his 250-pound sheepdog, who wore suede bootees John had thoughtfully made for him.
''The Cornish roads were bad,'' he said. ''The gravel at the verges was flinty and sharp, and mixed into it were splinters of broken glass. By the second day I had a slight preambulatory limp to one side. From that day till the end of the walk, I said 'ouch' every fourth step. Once, at night, I accidentally kicked a gigantic hedgehog and got two quills right up my toenail. Took the humour out of it, for a bit.''
Despite these privations, John managed to cover 12 miles a day. After four months and many odd encounters he hobbled into John O'Groats, where well-wishers awaited him. ''I'm seldom speechless,'' John said, ''but I just stood there without a word to say. I thought to myself, 'It is possible! You can do whatever you set your heart on.' It wasn't so much a sense of achievement I felt, it was more that I'd been led along by something greater than me. I have an intuition . . . when nature tells me something, I trust it, whereas I do not trust the established viewpoint, as it so often proves to be wrong.''
John has exasperated his way through three marriages and a number of relationships. Particularly trying was his penchant for living in a cave for four months at a time. Twice a day, as the tide roared in, he bundled his provisions and ran to the back of the cave. In the dark and briny damp, he listened, enraptured to the chatter of the wave-tossed pebbles. ''There is also a cathedral-like silence which helps me think. I'm addicted to harmony . . . restfulness. You realise the planet's breathing, that the same energy moving these stones is moving your heart.''
Now 60, his eyes a-twinkle with infectious enthusiasm, John no longer visits caves, much to the relief of his companion. His goal is to raise a million pounds for charity. He pours himself into getting support for the spreading of his new message, which emphasises the significance of vegetables, vitamins, and natural healing. He plans to deliver his views with Muddy the Frog, a large hand-puppet he created. So far he and Muddy haven't found their dream backer, but hope remains. Irrepressible spirits and optimism despite stimulatingly high odds are the eccentric's strong points. Oh yes, John's motto is derived from his canine friends: ''Wag your tail at everyone you meet.'' To be continued.
l Dr David Weeks is a clinical neuropsychologist and co-author of Eccentrics (Orion, #6.99).