Inside a London tower with a lofty historical pedigree

Most days, Chris Tookey sits in his octagonal study, over his octagonal sitting-room, and writes film reviews for a national newspaper, or adds touches to the latest musical he has composed, Romance. He is thinking of turning it into a musical book.

Chris Tookey has the bearing and delivery of a medieval friar, which is appropriate since the building he inhabits has been there since Henry VII first staggered triumphant off Bosworth Field. The brick tower was built in 1526 by Prior William Bolton. We know this because on the outside there's a bolt piercing a barrel, which was the prior's rebus. And this, Chris believes, makes it the oldest inhabited sitting-room in London - older even than Hampton Court Palace. "It was used as a garden house by the canons of Canonbury, and was originally turreted," he says.

He has a drawing of the area in earlier days that shows it as a leafy, rural spot where gentlefolk walked across the fields to take the air. Set into the outer wall of the priory is the little octagon. "We still have a bit of the old wall at the side, and another bit at the back," says Chris. Both are scarcely visible, draped as they are in ivy.

Today, the tower has a very handsome Victorian house wrapped around one side, and looks across Alwyne Villas to one of those delightful Georgian terraces that Islington does so well. It has an unusual storybook quality - full of different levels, staircases, hidden rooms and gardens - which comes across in the drawing by Ann Usborne in her book A Portrait of Islington. Selling it will be a wrench for Chris and his wife Frances, but they, their 14-year-old son Dan, and their large standard poodle Holly have all decided that they want to live in the country, so they are moving to Norfolk.

Prior William was clearly a formidable figure. He served as Henry VIII's Master of Works, supervising the construction of the chapel in Westminster Abbey. The area has always attracted a certain glamour - Sir Francis Bacon lived up the road in Canonbury House from 1616 to 1625, and Oliver Goldsmith lived in Canonbury Tower from 1762 to 1764. More recent inhabitants have included Dame Flora Robson, the actor-director Bernard Miles, and the former director-general of MI5, Dame Stella Rimington. "It used to be more bohemian, but values have gone up and it is all bankers and barristers now," says Chris.

"It is a fantastic house for entertaining because you can open up all the doors through the ground floor and spill out into the garden. We have had parties here for 300." You can imagine it. The rose-red octagonal sitting-room, the duck-egg blue kitchen-breakfast room, and the canary-yellow summer drawing-room are all connected by the tiled hall. "I always like houses that are bigger on the inside than they look from the outside. It is like something out of a story by C S Lewis," says Chris.

The garden is full of trompe l'oeil effects and surrounded by mature trees. "There is wonderful birdsong in the summer, which is marvellous to wake up to if you sleep at the back. We get some more unusual birds, too, such as kestrels, merlins and even parrots," he says. A formal area of pots and giant camellias rises, via brick paths and steps, to a wild garden trimmed with box hedging and yews in the process of being trained into decorative archways. The fernery is trimmed with snowdrops and bluebells beneath a copper beech that has yet to show its finery this year.

It is hardly surprising that the garden looks so good: Frances, who used to produce and script-edit television programmes such as Minder and London's Burning, is now a successful garden designer. And there is a wonderful surprise to come: a tiny gate leads into an enclosed communal garden, buried like a green lung between the roads, accessible only to the houses that back on to it. "You can have people round and flood out here on a summer's evening, or pull out a rug and have a bottle of wine," says Chris. "It is great for children, too. Our son used to run over the back through the garden to play with the little girl who played Hermione in the Harry Potter films."

So, the young Emma Watson can be added to the roll-call of famous inhabitants of Canonbury. Back to the house itself, there are five bedrooms upstairs, and a cupboard door opens to reveal a staircase up to a room on the top floor. Even the staircase is unusual - it looks as if it has been constructed out of huge wooden boxes, like a giant puzzle.

The engine room for Chris, though, is his enormous eight-sided study, strewn with books and papers. He used to work as a television director - with Peter Cook on Revolver, for example, which encouraged talents including Kate Bush, Dire Straits and the Boomtown Rats; and on the Channel 4 arts series After Dark. He is now film critic at the Daily Mail and has written 13 musicals, of which the most successful was Hard Times, which ran at the Theatre Royal Haymarket, and starred Brian Blessed. Chris plans to build a library on to the house in Norfolk. He will certainly need one.

The property is £2m, through Currell ( www.currell.com; 020-7226 4200)