As the small boat bobs through the dense mist off Anstruther, a squad of school children whoops with glee as a colony of seals appears through the haar. Others cling to the side of the May Princess, looking decidedly green. The vessel is heading for the Isle of May, a national nature reserve that is home to 12 species of seabird including puffins, terns and guillemots.

Andy Strangeway, also known as Island Man, is at pains to point out that, compared to his usual manner of gaining access to islands, namely jumping from moving boats and scaling sheer cliffs, this is child's play. Almost four years ago, the 41-year-old painter and decorator from Pocklington, North Yorkshire, set himself the challenge of being the first person to sleep on every Scottish island of 100 acres or more, a total of 162 islands. He describes it as the greatest adventure our country has to offer.

"This will blow, and the potential is phenomenal," he says with conviction. "The obvious thing to compare it with is bagging Munros, but this will be bigger than Munros because it will appeal to a cross section of people, not just athletic young lads. I love it when people say I must be crazy. I'm not athletic and, generally speaking, these types of adventures are done by middle-class people."

Something of a force of nature himself, Andy, never spotted without his trademark hat, has ensured that most of his fellow passengers on the May Princess are well-versed in his adventure before the boat has left the pier. This is his penultimate island. Only a flock of razorbills stand between him and his final goal of sleeping on all 162 islands: he has had to delay the trip to his final island, Soay in the St Kilda archipelago, until the end of the breeding season this week.

Andy has already had a taste of what this formidable archipelago has to offer. He is still flushed with excitement from his recent adventure to the neighbouring Boreray.

No-one has stepped foot on the island for years and its unforgiving geology meant it was the one that Andy had most concerns about. His fears were not unfounded. "You land and then you immediately have a steep incline for about 120 feet. My first experience of rock-climbing was on Boreray and I had no idea what I was doing." By chance, the previous week he had been shown how to use an ice pick to break a fall. It proved a life-saving lesson. "When I fell I didn't have time to think about it, but you ponder it afterwards," he says, tracing with his finger the cuts he sustained to his arm.

Leaving Boreray island the following day after spending a windy night in a tent proved no picnic either. "I didn't think I was going to get off the island alive because I couldn't find my way down. If I didn't have a GPS I would have gone 150m off a cliff. I've got no sense of direction."

Ruth, his wife of three years, occasionally travels to some of the more accessible islands with him but otherwise he is alone with his mascot, Clyde the bear. Financial constraints mean that he returns home to Yorkshire regularly to keep his decorating business ticking over. A significant number of the islands Andy has slept on have been uninhabited. "To some people that sounds like a nightmare, but I'm perfectly happy in my own company," he says, before admitting that the solitude has even allowed him to indulge in some nude sun-bathing.

When putting his plans into action, Andy has been at the mercy of the weather, and the advice of islanders has been invaluable. "The thing about what I'm doing is that you meet some fantastic people." He is beholden to the boatmen who agree to take him to far-flung islands. According to the 2001 census, there are 95 inhabited islands in Scotland with a total population of just under 100,000. While the total population of island-dwellers has fallen, the number of inhabited islands had increased from the 87 recorded in the previous census. According to the Scottish Islands Federation, depopulation is a very real concern on Scotland's islands, with the most acute case being Benbecula, which has seen a 30% drop in population.

When he set off on his mission, securing help was more difficult, and Andy almost abandoned his mission after visiting only 17 islands. "There were islands I just couldn't see a way of getting out to. Initially it was very hard to persuade people to take you all the way out to an island and then come back and get you the next day; people don't know who they are dealing with, you have to build up credibility."

One of Andy's most memorable trips was to Gruinard Island in the Summer Isles, dubbed Anthrax Island because it was used to test Britain's biological arsenal during the Second World War. Although the island was declared safe in 1990, some experts disagree. "I was told before I got on the island that the land where it the anthrax was is a slightly different colour. When I arrived, there it is: all different colours of green. It's amazing how much that plays on your mind, along with the fact that 95% of people that inhale it are dead."

Other challenges included failing to pitch a tent on Ailsa Craig during wild weather, and meeting a herd of feral cows on Swona, an island in the Pentland Firth that was abandoned in 1974. He was also attacked by birds as he tried to free himself from a bog, and believes he met ghosts when he heard the disembodied sounds of shouting and a dog barking on a now uninhabited island. The weather again got the better of him on an island near Orkney: after the boatman left, the force 6 gale turned into a force 11 storm and he was trapped alone on the island. "The tent I've got now, you could climb Everest with, but that tent should never have held. The storm lasted for six hours and it was absolutely terrifying. I fell asleep for an hour and when I woke up the storm had gone. It was an immense relief."

Despite having travelled to India more than a dozen times as well as visiting Ecuador, Zambia and Malawi, Andy's first visit to Scotland was only nine years ago. A subsequent visit to Dunoon sowed the seed of his island-hopping adventure. "Shortly after that, I was at an exhibition about explorers and I looked at all the profiles of people who were going up mountains and down rivers, but nobody had done anything with islands. When I asked a friend about it, she said it's because islands are inaccessible so it makes it impossible to do. You don't tell a Yorkshireman you can't do something," he says with a flourish.

So, what started as a fairly light-hearted challenge quickly turned into a mission and he is now poised to complete his adventure. He describes the experience as life-changing and has mixed feelings about it coming to an end. "It's quite sad in the sense that when you first arrive on an island, you never know what you are going to see. Because I've been on them all now I know what's coming - I will never have that experience again." He says it is almost impossible to single out his favourite islands. "I've no idea, it's something I would have to think about. Some of the ones I would list I wouldn't want to tell people about. If there are people there then forget it."

However, this is unlikely to be the last adventure for Island Man, who hints heavily about future projects. For the time being, though, it's back to Yorkshire and his decorating business. "My bank accounts needs some TLC now," he says.

marisa.duffy@theherald.co.uk

  • www.island-man.co.uk