‘It’s not my story, of course. It’s Blake’s story,’ says screenwriter David Nicholls of his latest project. Having cut his teeth on TV drama Cold Feet, Nicholls successfully adapted his own novel Starter For Ten for the cinema before he agreed to give Blake Morrison’s painfully honest memoir And When Did You Last See Your Father? the same treatment. ‘But although it’s someone else’s story, the way Blake wrote it made it into something universal, and it resonated with a lot of people, including me,’ says Nicholls. ‘So my job was to get that very personal story to work as a film without softening the material.’

Blake Morrison’s 1993 book was a candid and unsentimental view of his father, written in steely prose and with an uncommon emotional honesty.

‘When I was asked about any pet projects I might want to write, Blake’s book was one of the first things I thought of,’ says Nicholls. ‘At first I felt a bit daunted about working on it; my background was more to do with comedy than doing a straight drama. But I really wanted to adapt the book, and that proved to be the beginning of a four year process...’

To capture the essence of a largely internal struggle within the mind of the author, the book had the luxury of shuffling through Morrison’s memories in non-sequential order. But to generate the momentum required to keep audiences engaged in a film, Nicholls felt he had to connect the audience the same material but without resorting to cliche.

‘For me it’s very much a process of shaping material; the book is very ruminative, and full of personal anecdotes. Often poetic, it depends on incident rather than plot, and the last thing I wanted to do was impose some dopey Hollywood three-act structure on it,’ says Nicholls. ‘In a Hollywood film, father-son reconciliations are usually made up of unspoken tension, rows, a reconciliation and then death. But in this book, the death of the father is described in detail half-way through. So there was no way we could do that kind of tearful ‘I love you Dad’ ending, it just wouldn’t have been true to what Blake wrote.’

Morrison’s studied description of the differences and similarities he found in comparing his life with his father’s provided Nicholls with a chance to expand the tone of And When Did You Last See Your Father?

‘Blake’s description of the process of illness and dying is very moving to read, but representation of death cinematically can be a real test of the audience’s patience. So I did try to make the tone a little lighter, to create some warmth from the comedy of embarrassment,’ says Nicholls. ‘I wanted to keep hold of the bits which had most affected me – one example would be Morrison’s unflinching description of a disastrous camping trip he took with his father in the Lake District.’

The directorial responsibility fell to Anand Tucker, who helped Emily Watson and Rachel Griffith to Oscar nominations in Hilary and Jackie, 1998’s account of Jacqueline du Pré’s life from the point of view of her sister.

‘Anand had given me a lot of input with the script while we experimented with different ways of approaching the story, so I fully trusted him to make the script work,’ says Nicholls. ‘When I first heard about the casting, I was looking forwards to going out for dinner with Colin Firth, Jim Broadbent, and the others, but after the read-through, I didn’t feel I wanted to visit the set, I’d just have got in the way.’

And When Did You Last See You Father? also deals frankly with the less attractive ways in which individuals deal with tensions created by illness, and Nicholls admits he’s surprised by some of the content of the final cut.

‘While I always intended most of the dialogue to be pretty much as Blake wrote it, I was surprised that almost everything I wrote in the script ended up in the film,’ Nicholls says. ‘There’s a scene of Blake masturbating in the bath while his father lies dying in the next room; I really didn’t think they’d use the scene, but it’s very much part of the honest way that the book was written.’

Amongst the audience for the film’s Edinburgh International Film Festival premiere will be Nicholls’s father. What advice would his son give him about seeing the film?

‘I’m sure that he’ll understand that this is an adaptation, nothing to do with our own relationship,’ says Nicholls. ‘I hope he’ll enjoy it for what it is; someone else’s story.’

Dominion, 623 8030, 23 Aug, 8pm; Filmhouse, 25 Aug, 7.20pm, both £7.95 (£5.50)