The immortal Diana: Who's cashing in on the princess?

Feel the romance of British royalty – Diana underwear' was the slogan on billboards in southern China at the beginning of September. The curious image chosen by the Chinese underwear brand Jealousy International showed a lookalike of Diana, Princess of Wales, in a bra and knickers, with a tiara perched on her head. She was talking to a small child and, most bizarrely of all, she was playing a cello.

This is only one of a huge number of uses and abuses of Diana's name and image that have occurred in recent years and the announcement of Prince William's engagement to Kate Middleton, and more particularly his use of Diana's iconic sapphire for Kate's engagement ring, will certainly lead to renewed interest in his mother's life and death.

Representations on celluloid will probably prove to be the most far-reaching embodiment of the Diana brand. A cluster of productions are in the works. Tom Cain's novel The Accident Man, in which professional killer Samuel Carver is hired to cause the crash of a black Mercedes in a Paris tunnel in 1997 (on the assumption that the passengers are terrorists), has been optioned by Paramount. Irish actor and director Stuart Townsend has commissioned a screenplay from Eoin McNamee of McNamee's quasi-poetic novel 12:23 (a reference to the time when the fatal crash occurred in Paris) and development finance has been obtained from the Irish Film Board. As in The Accident Man, the Paris crash in 12:23 is no accident but the result of a conspiracy by intelligence agencies. Nonetheless, McNamee promises 'a thought-provoking and serious approach to what was a seminal event'.

In an as-yet-untitled Pathé project, Keira Knightley has been lined up to play Diana – the same company produced The Duchess, which also starred Knightley – and in a more quirky casting choice are eager for Helen Mirren (who played HM in The Queen) to play Diana's mother, Frances Shand Kydd, though the first Helen Mirren's agent knew about this was when he read about it in the press.

Finally, Renaissance Films is behind a £30 million production to star Oscar-winning actress Charlize Theron, Townsend's ex (they removed their commitment rings in January after nine years together), and Ewan McGregor. It is based on Diana: Closely Guarded Secret, the memoir by her former bodyguard Ken Wharfe (to be played by McGregor), who was by her side in public at all times throughout a period of eight years. 'We are intending to make the authentic movie of Diana by using the voices of the people who were there,' says producer Stephen Evans, whose credits include Henry V and The Madness of King George, 'and Ken Wharfe was right there at her side at the most significant part of her life.' The author of this screenplay, crime and children's writer Philip Kerr, is desperate to emulate the success Peter Morgan had with The Queen. 'The Queen, which cost £8 million and took £100 million, paved the way for this project,' Kerr explains. 'I wrote the screenplay 18 months ago. The thing that struck me about Diana, having spoken with Ken Wharfe and Patrick Jephson [her secretary], was that her intelligence was not much appreciated. She may have been ignorant, but I think she was as bright as her brother. I never met her, but I used to see her at my gym in Chelsea Harbour. She always looked glamorous, but also vulnerable, and that combination is very appealing to men. There's not an awful lot of glamour around these days. Still, if I was Prince William, I think I'd have had that engagement ring reset,' he tells me.

What exactly does Diana, the brand, represent that makes it so desirable to film-makers all of a sudden? First, and most obviously, there is the high-class and glamour element: she was a beautiful aristocratic woman whose look, especially the pared-down Nineties version, had memorable appeal, and her image was captured by the world's leading photographers. Then there is the aspect of noble victimhood, whether one believes she was the victim of a criminal assassination, of a tragic accident caused by the negligence of others, or merely collateral damage in a car crash. Then again there is the image of the outsider within the buttoned-up Royal Family, the emotional one who refused to tolerate the fact of her husband's mistress, and who dared to walk away from it all (though she could never ultimately escape, even in death). And finally there is her benevolence, the good works and causes that went beyond the mere charity tourism associated with many celebrities.

'It's a great cocktail,' says brand consultant Robert Bean. 'This coy feminine thing that appealed to men as well as women, an anti-establishment edge, and colossal world fame. So, contrary to modern, self-seeking celebrity, hers wasn't self-seeking for the most part. Her glow – her image, her brand – stood for good things and goodness more than anything else. When you compare that with the whole X Factor syndrome a mere 12 years later, it's a world apart.'

The problem is that Diana's brand is too nebulous for its own good and hard to monetise. 'I think it's quite a complicated brand,' says Peter York, a commentator on brand-related social trends. 'And also, at a practical level, most people who become brands in death are professional entertainers of one kind or another – Elvis or Michael Jackson – and there is a body of work and there is also a set of business arrangements and people who, in life, were guarding those business arrangements, and the whole thing is highly legalised and contracted out and so on.' The Elvis Presley estate was reckoned to be worth about $600 million in 2007 and the value of the Michael Jackson estate is estimated to be worth $4 billion, half from his 50 per cent ownership of the Sony/ATV catalogue and half from his own Mijac catalogue. 'There was some continuity. And here there isn't, because Diana didn't have product. The rest is everything and nothing. It's literally copping an attitude. It's like selling relics.'The trouble is that most of the Diana-related items being sold to the public are beyond the control of her estate. Take, for example, the latest Diana books. Next year sees the publication of Diana: Unfinished Business by Garrick Alder, a researcher and investigative journalist who had already helped Tina Brown with material for her book, The Diana Chronicles. Alder was amazed that Operation Paget, the Metropolitan Police investigation into her death, only devoted one sentence out of 800 pages to 'Squidgygate', the leaking to the press by the security services of tapes recording Diana's intimate conversations with a lover, James Gilbey. 'I would bet a goodly sum that Diana was under surveillance right up to her death,' Alder has said. He also believes that there were dark forces – though not the Royal Family – who had reason to welcome her demise. 'Diana was doing something historically unprecedented and politically very dangerous. She was drawing attention to the mechanisms of state that don't receive much attention normally. Britain's military-industrial complex is huge and goes right to the top – the Privy Council, which surrounds the monarchy, is stuffed full of military-industrial figures. The intelligence services play an important part in all this, supplying Britain with intelligence on world markets. Diana was shining a big spotlight on some of Britain's less admirable trades.'

Also published, in the US last autumn, was Female Force: Princess Diana, a comic aimed at children (or possibly the sort of trailer trash who feature in the American sitcom My Name is Earl). It tells the story of her life and death, and its core message portrays Diana as 'a fresh-faced addition to the historically stoic British monarchy'.

Another embodiment of the Diana brand is the travelling roadshow of her dresses – or rather, roadshows. Exhibiting at the Bath Fashion Museum over the summer were The Diana Dresses, a collection of ten memorable outfits including the black shift dress designed by Gianni Versace, which she wore to the Apollo 13 premiere, and a cream-pleated evening dress by Catherine Walker, worn for a Kathmandu banquet in 1993. According to the museum's manager Rosemary Harden, 'The clothes she chose to wear not only mirrored but actually led her on her journey from a shy teenager to a confident and assured woman.'