ALL around Raby Castle, the open countryside with roaming deer and autumnal trees provides as scenic a backdrop as any.

But when fans of the nation's favourite magician-turned-detective, Jonathan Creek, switch on their sets for a festive special edition, they will hardly recognise Lord Barnard's County Durham residence.

For as they take in Creek's own sleight-of-hand trickery, another kind of magic will have placed the castle on to a Scottish landscape with the help of computer-generated image (CGI) technology.

About 65 BBC Entertainment crew and 18 cast arrived at Raby last week and have been hard at work filming the episode, entitled Satan's Chimney.

The feature-length plot revolves around the making of a film in Scotland, during which the lead actress is shot dead in a room with nobody else inside and an entire crew outside the door.

This inexplicable murder must be solved with the help of Creek's singular talent, in what is said to be one of the best episodes of the programme to date.

In a brief glimpse of the filming, The Northern Echo saw stars Alan Davies and Julia Sawalha sit around a candle-lit table set in the castle's plush entrance hall.

Absolutely Fabulous star Sawalha has been drafted in because Davies' normal female lead actress Caroline Quentin decided to take time off to be with her family. Steven Berkoff is also among the cast. After about a dozen short takes Davies and Sawalha are captured, staring at a book, unmoving.

Between filming, both look bored.

Davies releases a big yawn, while Sawalha rests her head on her folded arms.

More interesting is the news of how Raby will be transformed into the fictional Doomdorf Castle.

Harriet Lawrence, the show's locations manager, first visited Raby some years ago with the Northern Screen Commission and returned at the end of July for another look.

After about 12 weeks of fruitless searching for a castle with a working drawbridge that could carry vehicles across a moat, they decided to opt for Raby as one of more than a dozen locations and use some CGI wizardry.

"What we were looking for was a castle in Scotland with a working drawbridge over a moat that you can drive vehicles across into a courtyard," said Ms Lawrence.

Raby didn't have the moat, or the drawbridge, but it had "one of the most perfect courtyards we've ever seen", she said.

"David Renwick, who writes the scripts, writes such perfectly tight scripts that we can't just take any element out when we are looking for stuff. The location is absolutely crucial," said Ms Lawrence.

The castle is no stranger to filming, recently featuring in the blockbuster Elizabeth, when it flickered across the screen briefly, but it will be more prominent this time around. CGI will be used to put the moat around the castle, while props have been made to extend walls and create the drawbridge.

At the end of this week, life at Raby - where staff have been involved with the shoot - will return to normal as cast and crew pack up and depart the North-East for their next assignment.

But they will not be leaving without having enjoyed the region's hospitality.

That included attending a football match at Feethams, in Darlington, where they are staying.

Arsenal fan Davies and a number of the film crew took in the Quakers' match against Rushden and Diamonds last Saturday.

Ms Lawrence said: "Everybody has been very welcoming and it has allowed the producers and director to feel very comfortable."