The importance of being able to pocket £50,000 for one's stately film location

As The Importance of Being Earnest opens this weekend, an unseemly row has broken out over the £50,000 fee to film at West Wycombe Park, the stately home used as the backdrop to the movie.

Since 1945, the Dashwood family, who built the handsome 17th century Buckinghamshire mansion, have lived there rent-free, as "guests" of the National Trust, which now owns the stately pile.

Now it has emerged the bulk of the fee will go not to the trust – but to the Dashwood family. The revelation comes amid ongoing controversy over the limited public access to houses such as West Wycombe, which opens for barely three months of the year and can never be visited on Saturdays.

Tom Watson, the Labour MP and member of the powerful Home Affairs Select Committee, said: "This is an insult to the millions who struggle to find a time when National Trust properties like West Wycombe are willing to accommodate them.

"These historic properties are preserved for the nation, not the landed gentry, and the opening hours should be at the nation's convenience, not that of the family who live there rent-free. Any money paid by companies for the use of the property should go to the National Trust. "

At the heart of the dispute is Sir Edward Dashwood, whose 18th century ancestor, Sir Francis, grew notorious as founder of the Hellfire Club.

The 37-year-old baronet charges between £2,000 and £7,000 a day for filming, and openly admits recent windfalls have enabled him to "tarmac the back drive" to the tune of £30,000 and buy new curtains for his domestic quarters.

He is now saving up to build a temple dedicated to his late father, Sir Francis, which is unlikely to be open to the public. And his future wish-list includes a fence around the family cricket pitch and a new deer park.

Sir Edward, who lives at West Wycombe with wife Lucinda, 38, and three children insists proceeds from film-making at West Wycombe are split between his family and the trust. However, he told The Independent on Sunday: "It's split according to what I decide. The idea is that it goes on the property, and the National Trust gets its share."

While admitting that the latest film had earned the estate around £50,000, he said such sums were tempered by the house's continual repair bill. "You only have to squeak with this building and it costs £100,000."

Asked about the restricted public access to the property, he said: "It's not open on Saturdays, but you can come on Sundays and Bank Holidays. We are open in the summer because that's when people most want to come.

"You could say, 'why don't you open all year?' Well, I'd move out and the trust would have to pay a curator and his wife instead."

This is not the first time the Dashwoods have profited from film-making. Clint Eastwood filmed part of his 1990 "African adventure" movie White Hunter, Black Heart at West Wycombe, and Ken Russell used it for his Tchaikovsky biopic The Music Lovers. As well as keeping a rein on filming rights, the Dashwoods have retained ownership of the sprawling 5,000-acre estate in which West Wycombe is set, and the antique-rich contents of the house.

"I provide all the furniture free of charge, and pay all the liability," said Sir Edward. Stressing that he pays "substantial" sums towards the upkeep of the property, and all its running costs, he added: "My grandfather negotiated to open once a week, on Wednesdays. I recently gave another month to open the grounds."

His protestations were dismissed as "outrageous" by Mark Thomas, whose Channel 4 show has exposed the lack of access to private art collections. And Paula Weideger, an American who has written a book on the trust and the landed gentry, said "Why are we maintaining these deals that were so cushy for families 40 or 50 years ago when large numbers who want to visit heritage properties are being kept out?"

Peter Nixon, the trust's conservation director, admitted that, with hindsight, some arrangements now seemed "anomalous". But he said many historic properties would otherwise have been demolished or have wealthy owners who might have barred all access and dispersed collections.

By allowing families to remain in their family homes, he said, the trust was presenting them as "living" buildings, rather than "museums".