It’s the email every writer dreams of getting: ‘I would like to make a film of your book.’ It came, out of the blue, at the beginning of July. And before you ask – no, it wasn’t Dreamworks or Working Title or anyone else I might have heard of. But I don’t care.

Jenny, my agent, and I have always thought that The Witness would make a good movie and now, six years after it was published, so does someone else – someone I’d never met until the other day, who loves the story enough to want to adapt it for the big screen. Even if it never actually happens, this still makes me feel pretty chuffed (a word I’d forgotten I knew until this moment).

Of course the road to the movies is knee-deep in the unexercised options of film rights. People snap them up and sit on them, sometimes even simply to stop someone else getting them. Then they can’t raise the money, or someone else comes out with something similar, or the theme goes out of fashion, or they just lose interest.

But my man is no world-weary Cannes veteran. Philip is young, recently out of film school, and is currently making a series of shorts. The Witness – I’m tempted to write will but I’ll settle for the conditional at the moment – would be his first feature. And what he lacks in experience he more than makes up for in energy, enthusiasm and the kind of chutzpah necessary to raise the several million quid it will cost to make. Though the thing that impressed me most about him is that he worked four years of nights as a security guard to save enough money to start financing his career as a producer (‘plenty of time to read’, he said).

Anyway, this coming weekend he and I are setting off for the central Highlands armed with a marked-up copy of the book and a handful of Ordnance Survey maps. We’re going to drive and walk some of the route taken by the protagonist, a young man called John MacNeil, and his eight-year-old charge, Ninian, as they flee across the Cairngorm and Monadhliath mountains, pursued by soldiers, in the civil war that rages in a Scotland of the not-too-distant future. (One which, I hasten to add, has no bearing on what I think an independent Scotland would really resemble).

Back in 2007, in the months following publication, the relentless round of secondary school visits was enough to take the shine off the story. This trip will undoubtedly bring it back for me. I look forward to that because it’s probably the most personal novel I’ve written: the Highland landscape and its traditional music, both of which I feel strongly connected with, are major themes in the book; the character of Ninian is heavily based on the son of friends; and the theme of civil war was a response to the Balkans conflict of the 90s, by which I felt deeply affected.

Also, The Witness was published just a few weeks after my father died. He was too damaged by the stroke that felled him to be able to read the book, which I regret since many of its themes were there because he had planted them in me. But he was aware of it and his final words to me, as I left his room for the last time, were ‘Good luck with the book, old boy.’

I think it was only in the latter stages of his life that he came to understand why I had chosen all the risks of being a writer rather than a more financially secure profession such as his, the law. But having grasped it he was rooting for me wholeheartedly at the end, and I like to think he still might be. If he is, he’ll certainly enjoy this weekend’s walkabout.

The Witness is currently out of print – though that will hopefully change when the film gets made! But it is available on Kindle and you may still be able to get one or two hard copies from Amazon