It’s all rather surreal, especially for Ian McEwan. The seafront of Redcar in North Yorkshire has been transformed into Dunkirk, 1940, and the words McEwan wrote in the privacy of his study, drawing on the experiences of his late father, a veteran of the British Army’s great escape, are being played out before his eyes in the film version of Atonement. It is movie magic, but also a vision of hell, and McEwan is as impressed as any of the thousands who have gathered to take a peek as one of the pivotal moments of the Second World War is conjured up at the British seaside. “It’s as if something has gone wrong with your imagination and you are starting to hallucinate,” says the writer. “It’s extraordinary. You sit in your study in silence and generate these words, and years later thousands of people are employed to bring it all to life. It’s odd how novel-writing can create employment.”

It can also bring a town to a standstill. Even those who aren’t directly involved with the production – the 1,000 local lads given a short-back-and-sides and dressed in the olive-green uniforms of the British Expeditionary Force, or the residents who have agreed to let their properties have a wartime Normandy makeover – are crammed at either end of a mile-long stretch of seafront, waiting to catch a glimpse of the action. There’s plenty to see. Today’s shot, a four-and-a-half minute sequence capturing the chaotic nightmare of the beach as soldiers wait to be evacuated, will form the centrepiece of the film, and if the buzz created by early screenings is to be believed, people will still be talking about it come Oscar time next year. For Atonement is not just good; it’s the best British film for a long, long time.

Director Joe Wright, a 35-year-old Londoner, has reassembled the creative team – producer, designers, technicians, leading actress Keira Knightley – who made Pride & Prejudice with him, to take on Atonement, a complex novel that many thought unfilmable. “Ian McEwan is a daunting challenge for any film-maker,” says producer Paul Webster. “His novel, Saturday, has been optioned and I wish the team all the best for that. Fabulous book, but hard to film. I thought Atonement was unadaptable too. Thankfully I’ve been proved wrong.”

Atonement was to have been directed by Richard Eyre with a script by Christopher Hampton. Eyre dropped out to make Notes on a Scandal, and then Working Title – the British production company responsible for a string of hits – asked Wright if he was interested. He was, and worked closely with Hampton on a revised script which, in structure, is much closer to the novel. McEwan himself takes an executive producer credit and has been happy to give input when asked, but wasn’t interested in writing the script.

“I’ve seen every stage of the script and I’ve given my notes on the basis that I know from my own experience [of screenwriting] that it is the director’s call and people will make the movie they want to make,” says McEwan. “So I’m interested in the process, but at the same time you can’t hang around being like the bad conscience of the whole project saying, ‘That’s not how it really was,’ or ‘That’s not what I meant.’ I think when you sign the rights over, you’ve got to let whoever wants to make the movie do it in their own way. You can chip in, but you have to let it go. It’s always going to be a different animal. A novel is maybe 10 or 12 hours of reading time and a film is a couple of hours. Shortcuts have to be made, character has to be established quickly and of course you lose all the interior quality of thought that is important to this particular piece. You have to cross your fingers, but I’ve already watched a lot of the rushes and I’m very impressed. I think Joe Wright has done a remarkable job.”

Atonement, mostly set in two time periods, 1935 and 1940, is an epic tale of the tragic consequences of a lie told by a young girl, Briony Tallis, a compulsive storyteller with a vivid imagination, and the havoc this visits upon so many lives – not least her own – as they are caught up in momentous events. The first part of the story is set in a country house in Surrey on a summer’s day and crackles with sexual tension between Robbie Turner (James McAvoy), the housekeeper’s son who has been sponsored through school and Cambridge by the wealthy family his mother works for, and the upper-crust daughter, Briony’s older sister Cecilia (Keira Knightley).

The next section of the story takes place in 1940, as Robbie and two comrades from his shattered regiment make their way to Dunkirk, barely staying ahead of Hitler’s advancing forces. Thanks to Briony’s lie, “Everything has been taken away from him – his life, his future, the woman he loves, everything – for something that he didn’t do,” says McAvoy. “And now he finds himself in the madness of Dunkirk and the evacuations. It’s terrifying and the only thing that keeps him going is that he has to get back to Cecilia. For me, this story is about tainted lives. It’s about the implications of actions. And it shows you how events unfold and how they change people’s lives forever. It’s an amazing story from an incredible storyteller, in the hands of one of the best directors working today.”

McAvoy is waiting to be called on set. We sit on the steps of Redcar’s cinema as nearby Wright and his director of photography, Seamus McGarvey, along with cameraman Peter Robertson, discuss the shot. The scene is ambitious, to say the least, and will involve Robertson carrying a heavy steadicam as he tracks McAvoy wandering through the surreal mayhem on the beach: brawling soldiers, horses being executed, army vehicles being destroyed (so the Germans won’t get them) and a Ferris wheel bizarrely turning in the background. But it works as powerfully as the opening sequence of Steven Spielberg’s Saving Private Ryan, set against the backdrop of the D-Day landings.

McEwan drew inspiration from the stories told to him by his late father, David McEwan, then a corporal in the Highland Light Infantry, later a Regimental Sergeant Major. “He did talk about those experiences in the year or two before he died,” says McEwan. “He had his legs badly shot up and rode a motorbike to Dunkirk with a soldier who had been shot in the arms. Between the two of them they managed to control the bike and they covered about 100 miles on it, but had to abandon it on the perimeter of the evacuation. I can’t help thinking he would have found this fascinating. I can’t help thinking, too, looking at these lads, how but for an accident of history, it could have been them on the beaches of Dunkirk, not their grandfathers.”

It is a strangely emotional experience to witness such a recreation, as McEwan points out. The extras, paid £50 a day, have wholly entered into the spirit and the set is “dressed” with such attention to detail (period cigarette packets, authentic labels on the beer bottles) that you have to remind yourself in a couple of days this will be contemporary Redcar once more and all traces of the Second World War, and the production, will have been removed.

“I would have done it for nothing,” says 20-year-old Philip Maughan, originally from Redcar but now living in the south. “My mum called me and said, ‘You’ll never guess what they’re doing to Redcar.’ I came back up to have a look and went along to be an extra. I’ve been meeting old friends on the beach – all dressed as soldiers – and it’s like a reunion. There’s a real camaraderie.”

Many of the extras have managed to smuggle in copies of Atonement and McEwan has been happily signing books. “A lot of them came up to me and had a little chat. It’s a long, tiring day, but they did it with such gusto and yesterday, at the end, in the fading light, there was a huge throng standing by and they gave Joe Wright three cheers, very lusty and well meant. It was quite touching.”

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