Diana: The film they should never have made

But you get the impression that, given their jumpy disposition, the people behind the production already have a fair idea what it's going to be.

Naomi Watts, who has taken the brave and some would say crazy decision to portray the people's princess, got up and walked out of a radio interview with BBC Five Live's Simon Mayo a few days ago.

The PR team who have been co-ordinating chats with the stars over the past fortnight have been heard nervously asking journalists before their one-to-one sessions: "You're a fan of theirs, right?"

And the leading lady has now left the country to escape the spotlight; she was spotted in a New York park over the weekend with partner Liev Schreiber and their two children, trying to remain low-key and blend in with the crowd.

It's little wonder folk are jumpy. The film, which opens to the public on Friday, has quite rightly been given a brutal panning by critics, who have branded it 'squirmingly embarrassing' and 'atrocious'.

It's a stinker, which would sit much more comfortably with the kind of cheap, tacky and unconvincing Mills & Boon-style romances littering daytime television.

The film purports to lift the lid on Diana's romance with surgeon Hasnat Khan in the final two years of her life, based on a combination of anecdotes, theories, and the pages of Kate Snell's 2001 book, Diana: Her Last Love.

The very private Khan, played in the film by Lost's Naveen Andrews, broke his silence to dismiss the project, saying: "It is based on gossip and Diana's friends talking about a relationship that they didn't know much about."

Hindsight is a wonderful thing, of course. Many felt Meryl Streep was crazy to take on Margaret Thatcher, Helen Mirren knew her role as The Queen could have gone one of two dramatic ways, and Nicole Kidman will be under the microscope when she becomes the late Grace Kelly.

But Diana's story is in a different league, and you have to question the wisdom of attempting to put a dramatic interpretation on the life of a woman who, even 16 years after her death, still features regularly on the front pages, courtesy of people from all walks of life who refuse to tolerate anything which may smear her memory.

Watts, 44, certainly mastered Diana's dulcet tones and mannerisms, but is ill-served by a tacky script crammed with cliches, childish dialogue and mood swings, painting the princess as an eccentric Bridget Jones-style singleton.

The actress admits: "I was very nervous about taking on the role. It's the biggest challenge of my career thus far. Taking possession of a character that everyone feels they know so well, and therefore belongs to them, was difficult and scary. Once we were filming, I was fully committed, but now we're back to opening it up again, sharing the film, and there's always that fear of how it will be received."

Although she was raised in Australia and has lived much of her life in the USA, Watts is actually British. She spent part of her childhood in Anglesey where Diana's son, Prince William, famously made a home for himself and wife Kate.

So has Watts been back there?

"I haven't quite found time to get back to Wales, no, but I have strong memories of my time in Anglesey," she says.

Locals would certainly be impressed with the Hollywood's star's grasp of the language.

"It has the most beautiful countryside, and I can still say Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch," referring to the town nearby, which has the longest place name in Britain.

Movies about the royal family have a patchy history. For every triumph like The King's Speech there's a turkey like William & Kate: A Fairytale Romance. But when the movie makers get them right, they're a passport for global riches. Such is the world's fascination with the House of Windsor.

The royal family has neither given, nor been approached for its verdict on the Diana film. To be fair, apart from a brief moment when a young William and Harry can be seen climbing into a helicopter, they don't feature in it.

But Ingrid Seward, editor of Majesty Magazine, believes it would make 'incredibly hurtful' viewing for for Diana's children. "They met Hasnat – well, certainly Harry met Hasnat – and I feel that once again their mother's memory has been hijacked."

* Diana opens at cinemas this weekend. Read an extended version of Carl Jones' review in Friday's Ticket supplement.