In life, Diana, Princess Of Wales divided opinion, so it's fitting that Oliver Hirschbiegel's drama, based on Kate Snell's contentious book Diana: Her Last Love, should have stirred controversy before a single frame has unspooled on the big screen.

Dr Hasnat Khan, the subject of the picture, publicly denounced Diana as a fiction, while a pre-recorded radio interview with star Naomi Watts ended abruptly with the suggestion that she walked out on DJ Simon Mayo.

Tittle tattle aside, Diana is a trashy made-for-TV movie, blessed with an award-winning German director and an Oscar nominated lead actress, whose talents are well and truly squandered. Both are undone by Stephen Jeffrey's clumsy script while Watts also lacks sexual chemistry with co-star Naveen Andrews, making a mockery of the tears and tantrums when the central relationship ultimately breaks down.

"I'll never be happy again, I just know it," whimpers Diana (Watts) to gal pal Sonia (Juliet Stevenson).

If the public image of the princess was elegance and poise, behind the scenes in Hirschbiegel's film she is emotionally cold and calculating, tipping off a tabloid photographer to her whereabouts so he can splash pictures of her on a yacht with Dodi Fayed (Can Anvar) and pique the jealousy of Dr Khan (Andrews).

Pathetic attempts to win Khan back take a leaf out of the book of Bridget Jones - minus the excessive smoking - including scenes of Diana attempting different dialects in the hope the doctor will take her call.

"Yes, I've been a mad bitch, yes I've been a stalker and yes I put on the clumsiest Liverpool accent to get your attention!" she concedes in one of many scenes that beggar belief.

Opening in Paris 1997, Hirschbiegel's film rewinds two years to sow the seeds of romance between the princess and Khan, part of which involves smuggling him into Kensington Palace in the back of her car.

"Looks about 80 kilos in there," quips one security officer as the vehicle passes a checkpoint.

"That'll be a Pakistani heart surgeon," deadpans a colleague.

The pressure of conducting a romance through the omnipresent lens of the media takes its toll and Khan eventually ends the affair, propelling Diane into Dodi's arms.

Diana isn't quite the total disaster some vitriolic critics have suggested, but it comes perilously close. Watts offers a passable impression of a global icon, rehearsing answers to Martin Bashir's questions in a mirror so she can perfect her head tilt as she whispers, "There were three of us in this marriage... so it was a bit crowded." Andrews fails to live up to his surgeon's nickname as Mr Wonderful and Hirschbiegel's direction lacks energy.

An excessive two-hour running time will test the patience of even the most ardent and devoted Diana fan.