THE Ardgowan Estate near Inverkip will take centre stage when new BBC drama Ordeal by Innocence airs.

An 18th-century house surrounded by 400-acres of parkland – on the coast in Inverclyde – it welcomed cast and crew over three months last summer, and again for a month in January.

When I visit during filming, the Palladian-style mansion has been transformed into Sunny Point, the fictional country estate at the heart of the Agatha Christie adaptation.

Egyptian artefacts line the study belonging to Leo Argyll, played by Bill Nighy (see main interview). A Christmas tree with blue and silver tinsel sits among the props (the story begins in December 1954) and there's an open coffin in one of the rooms (this is a murder mystery, after all).

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Quietly observing the hubbub around the house is Sir Ludovic Shaw-Stewart, the 12th baronet and owner of Ardgowan Estate which has been in his family since the 15th century.

Like many owners of Britain's stately homes, the 31-year-old has had to find innovative new ways to diversify the estate and keep things afloat.

He inherited Ardgowan after his father passed away in 2004, when Shaw-Stewart himself was 17. Four years ago, he left his job with international auction house Sotheby's in London and returned to Scotland to take over the reins from his mother.

Ardgowan Estate has since launched a whisky distillery and is marketing itself as a wedding venue as well as offering luxury overnight stays, fine dining, tours and educational courses.

The fortunes of the once crumbling Highclere Castle in Berkshire were famously turned around after it was used in Julian Fellowes' ITV period drama Downton Abbey. One can't blame Shaw-Stewart for hoping Ardgowan may enjoy a similar tourism windfall.

READ MORE: Bill Nighy on Agatha Christie, sex scenes and Scottish family ties

"It is a fantastic form of business income and publicity," he says. "Houses like this are a bit like the Titanic post-iceberg, so you need to keep them afloat. Like most old houses it needs a new roof down the line, it is an ongoing battle with the elements."

We're huddled in his office, talking in hushed tones as filming goes on nearby. "It is very exciting," adds Shaw-Stewart. "It is slightly like a circus moving into town – you are up there among the acrobats. It is fascinating to see how it all works, this very big, well-oiled machine."

This isn't the first time that Ardgowan has appeared on screen: it previously featured in Rebus, Taggart and Still Game – the classic episode when Jack, Victor and the gang attend a posh soiree – as well as more recently in Shetland and Jonathan Creek.

An influx of "set-jetters" – a nickname for fans who visit the locations where their favourite films and TV shows are made – would be wonderful, says Shaw-Stewart.

"I don't really know how to gauge the knock-on benefits of this production, but I hope there will be an upside to it. That would be the icing on the cake."

READ MORE: Bill Nighy on Agatha Christie, sex scenes and Scottish family ties

When we catch-up again once filming has wrapped, Shaw-Stewart reveals that visitors to Ardgowan will feel like they are walking into the footsteps of the actors.

"What is rather nice is we have kept a lot of the changes that were done for the set dressing," he says. "There was an element of redecoration for the programme and we've kept that. Sunny Point will live on long in our memories and within the house."

Ordeal by Innocence begins on BBC One, Easter Sunday, 9pm