There is a clever remote electricity generating system - everything works as instantly as if you were plugged into the National Grid - and full underfloor heating. Being so massive, the house retains its heat. I can tell you that on a cold wet Scottish winter's day, the warm floors feel pretty good. Outside, there is a sun-catching timber deck area with hot tub, built out over the rocky shore, and a broad jetty that doubles as a helicopter pad, sheltered by a tiny island. Water comes from a burn high in the hills.

As for the feel of the house inside, everyone says that that is wholly Cameron. "I'm really a traditionalist. I've always been drawn to old buildings," he says. "I like my houses to be cosy. I've stayed in very modern places, and I don't dislike them, but it isn't really me." So the spirit of the old croft is faithfully carried through, on a grander scale. The rooms are big - my bedroom and bathroom filled an entire circular floor at the top of the tower - but not ridiculously so. You get stone, cream-painted plaster and timber in interesting combinations. All the ironmongery, such as balusters and door latches, is purpose-made. Think Landmark Trust - that's top conservation grade interiors, the real British country-house look - but with buckets of added eccentricity. Such as the cantilevered spiral stair which swings up round the outside of the round tower - but within a tall, narrow hallway reaching right up to the roof rafters. There are bits of staircases linking levels everywhere, bits of slate roof inside as well as outside, as if the building has just grown piecemeal over the centuries. Mackintosh's own bedroom stair spirals up from the back of the living room in its own turret, complete with curved oak door at the top.