Corfe Castle is a toothachingly pretty place, the castle ruins and the town's old houses featuring on almost every box of Dorset fudge. The castle was once one of the greatest in England, built by the Normans and impregnable for more than 400 years. During the civil war, it was defended heroically, but unsuccessfully, by a tiny garrison under the command of its owner Dame Mary Bankes. The victorious Roundheads pulled it down; the walls were so thick that its destruction was probably one of the 17th century's greatest feats of civil engineering, although if they had waited only 50 years, developments in weapons technology would have rendered the castle strategically redundant.
After the Restoration, the Bankes family built their new home 15 miles north-east, at Kingston Lacy, near Wimborne, where the contours of the Dorset hills are softer and of no strategic importance. You reach the house along the B3082, one of the most beautiful roads in England: long, straight and with 365 mature beech trees standing on either side. Lawrence of Arabia, a fugitive from fame, often rode it at speed on his motorbike; no helmet, just a pair of goggles, the wind in his hair, the smell of burning oil. He believed that through speed you could lose yourself.
The beeches were planted in 1835 by Willie John Bankes, a great-great-great grandson of Dame Mary who was a friend of Lord Byron, and a talented artist. For much of the 20th century, this was as close to Kingston Lacy as you could get. No visitors were welcome. It was the most mysterious house in England, lost behind the trees, a decaying, overgrown palazzo housing one of the world's greatest private art collections.
Willie John filled the house with paintings and the garden with Egyptian antiquities. But he did not enjoy his home for long. Arrested after an incident with a guardsman in Hyde Park in 1841, he jumped bail and fled the country. As arrest warrants could not be served on Sundays, he often took an early-morning boat across the Channel to spend the day at Kingston Lacy, returning to France before midnight, or so it was said.
Over the next century, the family became increasingly odd and the house fell into decline. Its last owner, Ralph Bankes, lived in four rooms and kept the rest locked up. According to the National Trust brochure, he inherited his father's "solitary nature".
The last heir to Kingston Lacy was Ralph's son John. Like many summer days in Dorset, his life started brightly but soon clouded over. He took a double First at Oxford, but in his early twenties he began to lose interest in life.
When I first met him, he had just bought a house in Fulham, but although he often talked about having some furniture sent down from Kingston Lacy he never did, and he slept on the floor surrounded by books. The only things he brought over were some original Edward Lears, which he lent to his local pub, and a Botticelli drawing, which he hung in the kitchen.
John never locked the front door, because he had lost the keys. A Spanish language school took over the ground floor, uninvited or taking advantage of his good nature, and the Botticelli got stolen. About that time, Ralph decided that John was not a suitable person to inherit a large estate, and made over the whole lot to the National Trust - not just the house and contents but 16,000 acres, including Corfe Castle, hundreds of houses and cottages, and most of the Purbeck coast between Swanage and Bournemouth. The National Trust described it as a "most generous gift", as well it might.
I am probably in a small minority in thinking that the National Trust is not an entirely admirable organisation. Perhaps I am put off by the proprietorial and slightly superior air of the impeccably mannered grey-haired volunteers. I am uncomfortable with their unwavering determination to sign us up as members, like upper-class Jehovah's Witnesses.
Perhaps it is the whole business of conservation, turning real places into sterile theme parks. "The Tasteful Restoration of the House of Usher" would not have been one of Edgar Allan Poe's more successful short stories.
The trouble with lost gardens and houses is that people keep finding them. Every time I get back from holiday, I am only grateful that the National Trust hasn't stuck a large sign on my front door saying "The Lost Garden of Stockwell". My favourite gardens are neither formal nor wild, but feral, where bluebells and dog roses colonise the lawns and flower beds, and where there might once have been a path through the rhododendrons leading to a secret valley. It isn't the same when you put in neat gravel paths with a signpost saying "Secret Valley".
Kingston Lacy has been "restored to its Edwardian heyday", but has lost much of its magic, though I was pleased to find a picture of Ralph, whom I never knew. He looked a decent, honourable and rather lost person, much like John.
I wondered which of the attics had been John's room as a child, but the polite volunteer ladies had never heard of him. There was not even a photograph of him anywhere in the house. In the general restoration, he and his sister have been removed from the picture, and in the visitors' catalogue the family tree stops abruptly with Ralph.
The last time I saw John, he was wandering the streets, dressed in a tatty suit, his hair and beard long and uncared for. He never went back to Kingston Lacy.
The traffic was slow as we drove to the coast. Outside Poole, a large container lorry was parked between a couple of police cars, partly blocking the road. On the car radio, David Gray was singing: "What we gonna do when the money runs out?" Through a gap in the traffic, I momentarily saw two Afghans, handcuffed and kneeling on the grass, the expressions on their faces unlike anything you see in daily life, more like something you see in paintings. They were a long way from home, and now even further from the place they would have chosen as home. The police were wandering about, unconcerned: all in a day's work. Nobody cares about lost people.