Leading Article: Are questions of taste proper questions for a prime minister?

TACKY, tacky, tacky. The Barbie-style Diana dolls, the eight- inch plates sold under the rubric "May her light continue to shine", the television drama series, the instant book serialised in a so-called quality newspaper. Tacky is the right word: "adj (coll.), cheap or shoddy, vulgar and ostentatious, seedy".

Then there is Mohamed Al Fayed's ludicrous claim that he is 99.9 per cent certain that his son and the Princess of Wales were victims of a conspiracy by British intelligence agents. Even after making due allowance for the disorienting effect of grief, this goes beyond tacky into the twilight zone which is only a half-step away from alien abductions and the paranormal.

The Prime Minister is quite right that the "industry" which has sprung up around Diana's death is deplorable, but he is quite wrong to say so. Of course, the privacy of her sons - and of her other family and friends - should be respected. And, of course, William and Harry are bound to find the speculation about the circumstances of their mother's death upsetting. But in the end their best protection is openness and the truth, rather than suppression.

The problem with Tony Blair's intervention is not that his analysis is wrong. As his spokesman pointed out, "at the time of her death everyone talked about the need for a softer, kinder, gentler Britain in which we took account of the feelings of her children". Earl Spencer's searing attack on sections of the press at his sister's funeral jolted many tabloid editors into a show of public contrition and a promise of reform. "This seems to have been pretty quickly forgotten," the Prime Minister's spokesman observed.

How true. But the trouble with this observation is the implication that the Government is minded to do something about it, when Mr Blair's same spokesman only the other day went to considerable lengths to deny that there is any intention to bring in a privacy law either "by the back door or the front door".

Nor, we hope, does the Government intend to do anything about Mr Fayed. The linking by one Sunday newspaper of Mr Blair's comments with Mr Fayed's outstanding application for British citizenship smacked of a breach of due process.

More generally, though, Mr Blair's warning raises the important question of whose right it is to decide what is tacky and what is not. On these pages, for example, we have recently condemned the infection of historical publishing by all manner of trashy made-up theories, from pyramids built by extra-terrestrial visitors to lost cities of Atlantis. The publishing of conspiracy theories about Diana's death taps the same rich vein of popular credulity. While there is a moral responsibility on publishers, be they of books, newspapers, television programmes or Internet pages, to check facts and to apply the elementary test of scepticism, there can be no law against presenting barmy suppositions as historical fact.

There are limits on free speech, but loopiness is no grounds for its curtailment. There are limits of defamation, copyright, taste and privacy. (Despite Mr Blair's insistence that there will be no privacy law, privacy is already protected by the European Convention on Human Rights, and will be more so when this is actionable in British courts.) But none of these have been infringed by Mr Fayed, or by the journalists who have written a book about the Princess's death partly based on his testimony. The book "explores the possibility" that the Princess was pregnant - a possibility convincingly contradicted by her friend Rosa Monckton yesterday. That is the best thing to do with daft conspiracy theories: expose them to truth.

There is an analogy with the hysterical overreaction to the sale of "tacky" memorabilia associated with Diana-worship. This has brought forth calls for "regulation", and indeed now a system of "licensing" by the Diana memorial fund. However, as the fund has authorised plates "banded in 22- carat gold" and with a "numbered certificate of authenticity", its ability to tell tat from any kind of authenticity is questionable.

The problem with this, and with the fund's attempt to register images of Diana as a trademark, is that they seek to impose one definition of taste on a public which is entitled to decide freely for itself. The Patent Office should throw out the attempt to turn a public person into private property after her death. As the trustee Vivienne Parry said: "As a fund, we cannot tell people not to buy products. What we can do is put marks on products approved by the family."

What is worrying is the implication that, "as a government", Mr Blair should do more. Let us hope that Mr Blair, despite his eagerness to mount the pulpit, resists the temptation to tell people what they can buy, read and watch.