A SURGE in tourism because of TV drama Outlander is having a drastic impact on iconic sites associated with the series, its author has warned.

Diana Gabaldon warned that an influx of fans are damaging the local environment ahead of the fifth season which aired last night.

Tourism at historic sites which feature in the BBC show is “booming” with visitor numbers heading to Doune Castle, near Stirling, Scotland up by 200 per cent.

Gabaldon said: “We are very privileged to be able to use a lot of Scottish locations for the filming.

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“They are not film sets. They should be respected.”

She added that fans should “tread lightly” at Outlander’s historic locations also including Preston Mill, in East Lothian.

Raoul Curtis-Machin, operations manager for the National Trust for Scotland warned that tourists “had taken” their “toll on grass and gravel footpaths” at iconic sites.

Curtis-Machin also said souvenir hunters were taking iconic relics from landmarks.

Mrs Gabaldon added that she had recently been sent a letter from the US along with a package containing stones taken from Culloden Battlefield near Inverness.

Recalling the incident, she noted that the thief had apologised for taking the stones and asked if they could be returned to the historic battlefield.

She added of the incident: “To me, although you could not possibly condone anybody taking stones, the very gesture they sent them back is to me a mark of respect.”

Outlander follows the story of Claire Randall, a married combat nurse from 1945 who is mysteriously swept back in time to Scotland in 1743, where she is immediately thrown into an unknown world where her life is threatened.

There is encounters with the dashing Highland warrior Jamie Fraser - and becomes embroiled in the Jacobite risings.

Recent figures from VisitScotland reveal that Doune Castle saw visitor numbers have risen from 38,000 a year to 142,000, since the series started in 2013.

Meanwhile, at Blackness Castle at Linlithgow, another of the locations, numbers increased from 15,000 to 58,000.

Sam Heughan, who plays Jamie Fraser, the lead star in Outlander, has said Scotland had been “late” to capitalise on the “Outlander effect”.

Heughan said that tourism bosses haven’t taken the full advantage of the flood of tourists who have come to Scotland to explore the locations of the hit series.

Heughan added: “I think Scotland was actually kind of unaware of what’s been happening here for many years, I think we were under the radar a little bit.

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“I think finally they’ve realised, I think Scottish tourism has obviously risen dramatically.

“Doune Castle, that played Castle Leoch, home to the Mackenzie clan in the show, was up 600% in their tourism numbers, there’s so many now unofficial Outlander tours, there’s vast tourism here, so I think people are really realising and the Scottish government as well.”

At the same time, Gabaldon has also admitted that she would love to move to the Scottish Highlands following a recent trip to Inverness, the Highland Gateway.

Recalling the trip, she added: “We went to Inverness and booked into a small hotel on the river and we were just enchanted by that.

“It’s a small town. But it has got a very peaceful vibe to it.

“I grew up in a small mountain town, Flagstaff, Arizona, and Inverness has much the same feel about it. It’s just a very nice place.

“I wouldn’t mind living there.”

She added that the city had reminded her of her own hometown in the United States.