IT had all the hallmarks of a major cloak-and-dagger operation, up to the highest top-secret standards of Special Branch, MI5 and the Secret Intelligence Service. But all they were doing was making a film – and not even a James Bond one at that. Staff on

IT had all the hallmarks of a major cloak-and-dagger operation, up to the highest top-secret standards of Special Branch, MI5 and the Secret Intelligence Service.

But all they were doing was making a film - and not even a James Bond one at that.

Staff on the set were staying tight-lipped about what was being filmed and even a bemused neighbour confided: "I've been told to say nothing about what is going on."

Centre of the hush-hush op was an isolated old barn and apple orchard stuck in the middle of the desolate Fen flatlands near Walpole St Andrew.

It had been chosen as an ideal location for shooting scenes for the film Atonement, starring Oscar-nominated actress Keira Knightley, who was nowhere to be seen this week.

Publicity executive Rachel Kennedy, who was tracked down to her office in one of about 20 luxurious caravans at a plush base camp set up about a quarter of a mile from where filming was taking place, said: "She won't be here today. She completed filming a couple of weeks ago."

Thirty girls from the Sandra Reynolds Agency, at Norwich, are being used as extras in the filming, acting as French-type schoolgirls with "an innocent look" for one of the film's harrowing scenes.

With entry to the set strictly forbidden to outsiders, just about all that has been seen of the filming in the thickly-wooded apple orchard from the roadside about 50 yards away has been clouds of smoke drifting across fields.

Despite the secrecy, producer Paul Webster was happy to reveal why this area had been chosen for one of the locations.

He said: "The beautiful Norfolk and Lincolnshire landscapes are very similar to that of Dunkirk and northern France, and it gives us the opportunity to make the best of an extraordinary landscape."

Location manager Adam Richards said: "Having looked at more than 20 locations, we came across Walpole St Andrew and it was perfect for what we needed.

"The added bonus of this location is that we were able to find a property on private land where we could shoot both exterior and interior scenes."

One person keeping a keen eye from the sidelines on the activities of the film crew was neighbour Georgina Wright, 50, who has lived next to the site for 28 years.

She said: "It has been really great to watch them. They came and asked permission to park their vehicles and have been very nice.

"I haven't seen anyone well-known but I have been asked not to say anything about what is going on.

"There has certainly been a lot of activity - normally this is a very quiet place, one of the most peaceful spots I know."

Atonement, based on the novel by Ian McEwan, is about a 13-year-old girl and her Cambridge-graduate older sister Cecilia Tallis, played by Miss Knightley.

Much of the story is set in France in 1940 and deals with the horrors of the Second World War.

The director is Joe Wright, whose partnership with Miss Knightley on Pride and Prejudice earned her an Oscar nomination. The actress also starred in the recently-released Pirates of the Caribbean: Dead Man's Chest.

Also starring in Atonement is James McAvoy, who starred in The Chronicles of Narnia, Brenda Blethyn and newcomer Saoirse Ronan, who plays Briony, the sister of Miss Knightley's character.

Atonement is the latest British movie in a long line of leading British films from the company Working Title Films, which also produced Notting Hill and Bridget Jones.

Filming at Walpole St Andrew is now complete, but shooting is scheduled to continue in locations in other parts of the country, including Shropshire, London, and Lincolnshire, until the end of the month.