Allowing film crews into heritage sites brings in income, in location fees and the knock-on increase in visitor numbers, as well as revenue to the local economy.
But with some of the UK's most precious built and natural heritage looked after by the trust, staff have to be careful that properties ranging from stately homes to Sites of Special Scientific Interest (SSSIs) are not damaged by filming.
Cut-open tennis balls under tripods and corrugated plastic on the floor are just some of the tricks used to protect historic houses.
During the filming of the forthcoming version of Robin Hood, directed by Ridley Scott and starring Russell Crowe, at Freshwater West, Pembrokeshire, all the horse dung had to be picked up and removed to prevent new bugs being introduced to the nature site.
The trust's media and broadcasting manager Harvey Edgington said the organisation has been "proactively" promoting properties to film companies since 2003.
The trust made the switch from "waiting to be asked" to promoting its properties as potential film sets because location managers were only thinking of stately homes, he said.
"We also have 600 miles of coast and mills, cottages and farms, as well as sites such as the White Cliffs of Dover and the Giant's Causeway."
It is a policy which has paid off, with the film unit bringing in 5m since November 2003 – all of which goes back to the properties where filming occurs.
Around 60 sites are used each year, with around 50 feature films using National Trust locations over the past decade and bringing in an average 4,000 a day for the property.
It includes Fountains Abbey, in North Yorkshire, which was used in the film adaptation of Alan Bennett's The History Boys in 2005, and also for the finale of the award-winning TV series Fat Friends.
The film version of Pride And Prejudice, starring Keira Knightley, helped boost visitor numbers to Basildon Park, Berkshire, by 75 per cent.
Miss Potter, in which Renee Zellweger played Beatrix Potter, prompted an increase in visitors to both the real Hill Top, where many of the children's author's stories were written.
When Alice In Wonderland is released this week, the National Trust is expecting Antony House in Cornwall will follow suit, and could even see a three-fold increase in visitors.