Do you shape your life around the home you live in or move house to fit your changing circumstances? Writer Anthony Horowitz appears to be taking the latter path, shifting from a big house in suburban north London to a groovy empty-nesters’ penthouse loft in Zone One. Not that his nest is empty yet, but his teenage sons can’t wait to leave Crouch End for Clerkenwell, and his wife, television producer Jill Green, is also looking forward to a glamour upgrade with skyline views.

Horowitz, however, has a serious case of cold feet.

“This house is where all my best work has been done,” he says. “Obviously, I’m part of this decision, but it’s a big wrench. I can’t stand the thought of leaving. I’m so depressed about selling, I think we’re completely mad. And this is where Alex was born.”

Alex, as any young lad who has ever opened a book voluntarily will tell you, is Alex Rider. The hero of six bestselling adventures, he is a 14-year-old secret agent who combines the derring-do and gadgetry of James Bond with the wholly realistic attitudes of a teenager. The first Alex Rider film, Stormbreaker, opens in July. As well as his remarkable feats as a children’s author, Horowitz has a long track record in scriptwriting, with many a Midsomer Murder to his credit, and he’s working on the next series of Foyle’s War, to be produced by Green.

But he still feels his success is intimately connected to, and inspired by, his home, and frets that it might not survive the move from the house he and Green bought 15 years ago. They had sold their maisonette in Wandsworth Bridge Road, Fulham, and were renting while they looked for their next home.

“I don’t understand the property market and I don’t even believe in it,” says Horowitz, 50, who is asking just under £1.6m for their six-bed, four-storey place. “But this is my one property tip: rent between selling and buying. It’s the best way you can spend money in the world. We only got this house because we weren’t in a chain. We paid £350,000 for it, way more than we could afford. We had to mortgage ourselves silly.”

It was worth it: he knew it was somewhere he could write. “I was beyond working in a bedroom any more. All we wanted was a place with a separate building for me to work in.”

They’d looked all over Richmond, Barnes, Putney and Fulham and had been shown “a boathouse with three walls; sheds; disgusting granny annexes” before they discovered the brick-built two-storey outbuilding tucked into a corner of the Crouch End garden. “It was 15 miles from where I wanted to live, but I had to have it.”

The annexe has a bedroom, bathroom and kitchenette and, most importantly, a room large enough for a substantial office. The view from his black L-shaped desk is through picture windows to mature trees that fringe the peaceful garden. “I’ve sat for so many hundreds of hours behind this desk. Where I am is what I write,” Horowitz says. “Everywhere in this room, there is something connected with my work.”

There’s the model crane he needed to create a scene in Point Blanc, a magic trick, a human skull “Even that umbrella plant my wife hates and wishes to see dead has been growing with me all the time.”

I suggest that the view from the studio being built on the roof of the new pad might offer fresh inspiration, but he’s not quite ready to be convinced.

He enjoys having the house to himself when he needs a break. “I like the idea of being lost in this rather large house, rattling around, playing the piano.” He can mooch back across the lawn into the light and airy kitchen diner extension he and Green added, or pick out a few tunes on the grand piano in the gold and cream music room, connected by glass doors to the library, with its richly dramatic dark green and deep red decor, where he can read or watch television. And all over the house are his treasured mechanical toys, intricate wooden gizmos with handles and levers that transform little men into little ladies and other equally sweet but silly tricks.

They’ll be making the trip to Clerkenwell, but otherwise precious little will survive the pre-move decluttering. “We’ll get rid of nearly everything.” He’s starting to cheer up a bit. “I’m going to be travelling more, so having a flat you can close the door on makes sense. Jill is right, we need to move on.”

Though he denies being part of the “sandal-wearing Crouch Ender” community, the solitary writer nevertheless declares that “for 15 years I’ve always got on with my neighbours. Everybody looks out for each other”. So, in a defiant last gasp, as he bravely faces the Clerkenwell future, he declares: “So I’m not going to sell to anybody who isn’t nice!”

Anthony Horowitz’s house is for sale for £1.595m with Foxtons, 020 8829 4040, www.foxtons.co.uk

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