It's time to come out. And half-way between Sunday night's BBC documentary, How Diana Died, and the publication of Lord Steven's report offers as good an opening as any. I'll admit it straight: along with 30 per cent of the British population, I simply cannot be persuaded that Princess Diana's death was an accident.

Oh, I know the very juxtaposition of the words "Princess" and "Diana" marks me out as a commoner - and therefore unreliable in such matters. Those really in the know speak scrupulously of "Diana, Princess of Wales". And the establishment, joined for once by the metropolitan chattering classes, has done its best to dismiss us sceptics on the Diana question as fantasists and fools. Perhaps we are.

Then again, look at the delays. Look at the elements that still have to be explained. Look, finally, at the efforts "they" have applied, even at this late stage, to trying to "prove" us wrong.

We know that French police and French ministers might not be the easiest partners in an investigation. We suspect France might not be the best-ordered country in a crisis such as the one that brought the mortally injured princess to hospital in the small hours of the morning. But why has it taken the best part of nine years for an inquest to be held? Why did the Fayed family have to threaten court action for even the preliminaries to the inquest to be held in public? If any death is of public interest, surely it is that of Diana. Then those nagging details. It concerns me not at all whether Diana was pregnant, and if so, by whom. I am profoundly uninterested in Dodi's intentions when he bought that ring. I am not even sure that the prospect of the Fayeds being brought into the royal circle supplies a motive for murder. Other things trouble me more: the small, elementary things that do not add up.

Why were none of the CCTV cameras at the Paris Ritz working that evening? What about that small white car that some saw in the tunnel? Why should the driver, drunk or sober, have been in the pay of the French secret services, and why - as we now learn - were Diana's phone calls monitored by US intelligence? Why did it take so long to transport Diana to hospital? What about the speed with which the tunnel was cleaned, and why were Mercedes mechanics not permitted to examine the car?

Time and again we are told that the conspiracy theory has been discredited. But it is not discredited just because the BBC reports DNA evidence that "proves" the driver's blood sample was really his. Drunk or sober, an agent has his uses. The BBC protests too much. By leading the weekend news on this detail, it imposed argument on fact. I felt hectored by an item that essentially promoted Sunday's documentary. This, too, was strange. How Diana Died was the first of a series on conspiracy theories. It was shown the weekend before Lord Stevens publishes his report. How neatly it all hangs together. If the Diana conspiracy is classed as just one of a half a dozen daft theories swallowed by the gullible, it must soon be discredited with the rest.

This conspiracy, however, is not so easily dispatched. Diana herself claimed that there was a plot to kill her in a car crash less than a year before she died, and the method is a staple of security services the world over. My personal conspiracy theory stops short of suggesting who did it, but motive there surely was. By breaking free from the Royal Family and behaving as indiscreetly as she did, Diana was subverting the monarchy, and thus the state.

The establishment may have underestimated the threat to the social order from her untimely death, but what of the destabilising effect had she lived? With the hindsight of 10 years, it can be said that the standing of the Royal Family has benefited from the absence of Diana.

I do not generally favour conspiracy theories, preferring the cock-up school of history. I never blamed the US government for the Oklahoma bomb and divined no darker secret behind the planes that smashed into the World Trade Centre. I don't see Dr David Kelly's death as anything other than suicide. I don't even believe the Prime Minister lied about Iraq's lethal weapons; I fear he believed in every last tonne. Nor can I offer any explanation for the poisoning of the former spy, Alexander Litvinenko. I just do not think it was in Putin's interests to have ordered it.

Diana's death is different. There has been too much secrecy. Too many people have tried too hard to convince us we should not believe what we do believe for us to accept that it was only an accident. Which reminds me of something else I don't believe: that only one in three Britons shares this view.

m.dejevsky@independent.co.uk