This time it wasn't the butler that did it

Surely the investigation into Diana's crash should be shown 24 hours a day on a reality TV channel. And the climax should involve all the royals being led into a drawing room, where a detective stands in the middle saying: "The difficulty with this case is that every one of you had a motive." Then he slowly reveals the results of his inquiries, occasionally saying something like: "When I found a manual on how to destroy brake pads hidden under the Imperial Crown, I suspected you, Elizabeth." To which they would make replies such as: "Why, inspector, that's preposterous."

Eventually the culprit would be accused, shift nervously and say: "But inspector, you haven't a slither of proof," before making a dash for it, then snarling: "Yes, I DID do it. And why shouldn't I? Have you any idea what it was like watching her float about with millionaire Arabs, while I was stuck here greeting the President of Uganda?"

Sadly, however, the case has been handed to the chief of the Metropolitan Police, so instead there'll be a four-year inquiry costing £40 trillion in which they'll try to pin the murder on an unemployed dustman, until the case collapses when it emerges that he spent the whole of 1997 in intensive care following an accident with a wheelie-bin.

The potential for entertainment is boundless. Already a coroner of the Queen's household has made the statement: "She wasn't pregnant, I have seen into her womb." So imagine the evidence when they call the bloke who did her colonic irrigation.

And Paul Burrell is certain to see this as an opportunity to make a few more quid. Perhaps he'll team up with Ben Elton and stage the whole thing as a musical. They'd only have to modify it slightly from the one about Queen, changing the lyrics to "Crash - ooah aaaah - in the underpass," and "I wish I'd gone by bicycle, I wish I'd gone by bike."

One newspaper has objected to the inquiry, suggesting it will be "too painful" for the Royal Family to go through the episode again. Which would be strange, because they didn't seem to give a toss at the time. As I recall, on the morning Diana died they carried on with their normal engagements, making no comment whatsoever. The Queen didn't even say something like: "Oo dear, well we've had Eileen over the road go in July and then Mrs Diddlehurst in the post office and they SAY these things come in threes."

The official view on Di's famous letter, in which she pondered whether Charles would murder her, appears to be that it's a sign of her "disturbed mind". Indeed, how could anyone trust her scatty ramblings, as opposed to the sane and rational thoughts of someone who talks to plants and wishes he was a tampon?

The real problem with the conspiracy theory is that while it may be exciting, it's also mad. For example, the main puzzles are why the ambulance took so long to get to the hospital, why the CCTV cameras in the tunnel were facing the wall and why the area of the crash was quickly sprayed with disinfectant. This is peculiar, but if this was how the royals did it, they must have copied the plan from an episode of Mission Impossible. Maybe Prince Philip broke into the ambulance station, karate-chopped the supervisor and took over the switchboard, Edward dressed as a workman from the council and twisted the cameras and the Queen Mother stalked through the sewers so she could pop up and disinfect the road.

As a method of murder, it's extraordinarily elaborate, and that's what's wrong with it - the state is simply not that clever or efficient. The tragedy of most conspiracy theories is they assume the authorities to be all-powerful. A murder along these lines would involve so many people they couldn't risk it, in case someone one day broke rank. Which is why you can't help but glaze over when they say things like: "Ah, but it wouldn't be hard to hire a suicide chauffeur - check out the website with a copy of a receipt to Prince Charles from Osama Bin Laden." Or: "The CCTV of her and Dodi in the jewellers is fake, because her ring is on her second finger and she always kept it on her third finger so they're decoys, they were already dead ..."

On the other hand, they managed to cover it up for 50 years that grand-dad was a Nazi, so they've got a bit of experience. And you could argue that, as royals, feuding with rival families is in their genes. Perhaps that's what's on the missing tape of Charles - he's booming: "Are we to bleat like lambs while our enemy seeks alliance with the wretched Al-Fayeds in order to pass scorn upon our name? Then sally forth my brothers, re-position the CCTV cameras, hire an untraceable Fiat Uno, and in the name of God we shall triumph."

But the main reason why the murder theory can't be right is you know Philip could never have had anything to do with a scheme like that. He'd have yelled: "CCTVs and disinfectant? What a load of cobblers. Just fetch me my twelve-bore and I'll blast the old bag."