Hollywood stars were an unlikely addition at Barnet Council’s offices when they took part in filming for a new movie that was released this week.

Keira Knightly, Kevin Costner, Sir Kenneth Branagh and Chris Pine all descended on the North London Business Park in Brunswick Park to shoot scenes for Jack Ryan: Shadow Recruit.

Council staff were sworn to secrecy over the covert filming, which took place in October 2012, but with the movie’s release this week, details of the A-listers’ visit have emerged.

The local authority’s offices were transformed into a CIA medical recuperation clinic, named the Walter Reed Army Medical Centre in the film, which stars and is directed by Kenneth Branagh.

In the movie, Chris Pine, who plays Jack Ryan, recuperates at the centre after an injury, and co-stars Keira Knightly and Kevin Costner were also present for the filming.

A 75-foot crane with a 500-ton lift was erected at the council headquarters off Oakleigh Road South to suspend a rig of sprinklers used to shower rain effects down on the set when crews filmed training scenes in the internal courtyard.

Large amounts of water were pumped into the courtyard for the special effects and crews were forced to take extra precautions to prevent any flooding in the below ground basement rooms.

A council spokesman said: “It was exciting to have such big stars in the business park. We were told strictly not to take photographs of them filming but it created a bit of excitement.”