Everyone, as Oscar Wilde said, should have a hobby. And that includes royals. It was strangely reassuring last week to discover that the Princess Royal was just as in thrall to eccentric pursuits as the rest of Britain seems to be.

The Princess’s vice is collecting Scottish lighthouses. So far she has visited 53, many of them in her role as patron of the Northern Lighthouse Board, the body that looks after all the beacons around Scotland’s coast. But, according to reports, Anne has now set her heart on seeing the remaining 148. Her interest appears to go beyond duty. One local on the island of Oronsay is said to have described the princess and her husband, Commander Tim Laurence, as a “couple of chancers” when she turned up unannounced and asked to see his light.

Apparently, she’s been doing it for years. In 1956 — when she was only five — Anne accompanied the Queen on a visit to Tiumpan Head in Lewis. Charles got to blow the foghorn, but it was the princess who seems to have been hooked. In 1998, she was present for the final shift of Scotland’s last manned lighthouse in Fair Isle. Last week she was out looking at lamps off Scotland’s east coast; later in the month it will be Skye. “It’s a perfectly normal hobby,” one royal insider commented. But is it? Does Anne really know where her interest will lead her? Little in the world of pharology — the technical term for the study of lighthouses, derived from the Pharos light at Alexandria, one of the Seven Wonders of the World — seems entirely normal.

PERHAPS the princess should ask Peter Hill. He knows as much about lighthouses as anybody. As an art student in Dundee in 1973, Hill applied for a job with the Northern Lighthouse Board after answering an advert in The Scotsman. By his own admission, he was an unlikely person to entrust the nation’s shipping to, a 19-year-old hippie with a collection of Captain Beefheart records and a love of the novels of Jack Kerouac. But since childhood he had wanted to be a keeper. “Next best thing to being a spaceman, probably better,” he says.

Stargazing, his very funny account of the summer he spent working the lights at Pladda, Ailsa Craig and Hyskeir, does a good job in explaining the fascination. On a calm day, he would sit with one of his fellow keepers, skimming stones across a millpond sea and speculating about what happened to the three Flannan Isles keepers, who in 1900 disappeared from Eilean Mor without a trace. At night, between tending the light he would, if time allowed, write haikus or dip into Treasure Island.

“But the most magical moments happened when we changed watches. There was an unwritten rule that the keeper about to head off for bed would stay up for an extra half-hour and engage in conversation with his colleague in order to help him stay awake.”

During the changeovers, Hill would listen to tales of the lighthouse service’s most eccentric keeper, Lachlan Fairbairn: “Soon as he arrives on a light, the first thing he does is take all his clothes off,” his fellow keeper Ronnie told him. “Spends the whole month buff naked. It’s a frightening sight, especially if he’s frying sausages.”

Or perhaps he would discuss the 94-year-old keeper of the original Edison lighthouse near Plymouth, who single-handedly fought a fire while his assistants lay drunk on gin below, before accidentally swallowing seven ounces of molten lead. (The ingot later ended up in the Museum of Scotland.) For a young hippie wanting to become a writer, the attraction was obvious. Lighthouse-keeping, Hill says, was one of the few professions where you got paid to tell stories, to stop your colleagues falling asleep and, though he went on to become an art critic, he has never lost his passion. For his forthcoming book, Ocean Necklace, he has just spent two years travelling the lighthouses of Australia, New Zealand and Samoa, trying to record the old keepers’ tales.

“Halfway through into this project, I coined the term, ‘horizontal mountaineering’,” he says from his home in Melbourne. “You leave the big city and travel along the coast, passing towns and villages, then lonely outcrops with occasional houses, until eventually you come to a lighthouse surrounded by cliffs and ocean. This is the equivalent of at last reaching a mountain peak. I liken it to wanting to climb all the Munros in Scotland. There is definitely a growing trend towards ‘bagging’ lighthouses. It sounds like Princess Anne has the bug.”

In Australia, he says, the pharology boom has been driven by the “grey nomads”. “That’s what we call these retired couples from 50 years upwards who have seen the world but have never really seen Australia,” says Hill. “We have convoys of them diving around the continent, and as they go many visit lighthouses on the way. The fact that they’re all now automated has only added to the romance — the knowledge that a long era has come to an end and that, to use a rather tired phrase, ‘the light is on but nobody is at home’. Perhaps in visiting a lighthouse we are, in our own small way, bringing a human presence back to the tower.”

Perhaps. Sometimes it seems more like an obsession. Last July, the United States Lighthouse Society held its summer expedition in Scotland, a trip that involved bagging 27 lighthouses in 15 days. Inevitably with this rate of spotting, some of the visits were perfunctory. More precisely, some of them weren’t even visits, as Diana and Don Carter’s slightly Pooterish online journal shows:

“July 18. 9.10am. We arrived at a spot where you could see the Inchkeith Lighthouse off shore. This is a photo opportunity, and not a very good one at that. We left five minutes later . . . 1.15pm. We got closer to the Fidra Lighthouse, but there was no time to stop for photos, much to Don’s dismay.”

Things did not improve the next day, during which they had just 10 minutes for Tayport High and Low, 15 minutes for Elie Ness, and further disappointment off the Fife Coast: “6.35pm. The boat docked back in Anstruther. 6.50pm. The buses left. We did not even have time to visit the Fife Ness Lighthouse! Another bummer!” Which is a polite way of putting it when you’ve paid several thousand dollars and travelled from Detroit for the privilege.

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