Sarah Sands: Out of the shadows and into obscurity

Belle de Jour made a big mistake revealing her identity. Among the ranks of anonymous authors, she above all should know that the thrill is in the chase. Once the mystery is gone, the fun is over

The decision by Belle de Jour to out herself was taken because anonymity was "no fun" any more. She could not enjoy the glamour of her success, she was not even able to attend her own launch party.

Dr Brooke Magnanti got the attention she craved, although the wind changed direction after the first day. The beauty of her secret was that she controlled the narrative of her life. Here she was a research scientist with the alter ego of a courtesan. How could you not be a little in love with your creation?

At first, journalists took her at her own description. The Times said that she was a "respected" specialist in developmental neurotoxicology – I am impressed that its staff were able to tell, for it is not a field that I would feel competent to judge. The pictures were also a relief. Dr Magnanti was foxy without looking, well, tarty.

Then Belle de Jour, played on television by Billie Piper, lost her hold on the plot. Newspapers introduced new characters, including a peculiar father who pursued prostitutes. Columnists rewrote Belle de Jour as a deluded head case. By the end of the week, the brainy, socially defiant beauty had become pitiful. Dr Magnanti is reportedly writing a novel under her own name. I wonder if her publishers will bother with a launch party.

The error of understanding was that exposure would be more potent than anonymity. Surely Belle de Jour of all people would know that the thrill is in the chase. Every femme fatale from Anne Boleyn to Annabel Goldsmith has discovered that once a woman is conquered, the hunt moves on. Familiarity is the killer of sexual allure, but diminishes other qualities too.

Salam Pax, the Baghdad Blogger, was the voice of honesty and courage during the allied bombardment of 2003. If he went quiet I would draw breath; once he was back on line I would will him on. He blogged because he had something vital to say, he was Everyman among Iraqi citizens with the individual advantage of being an accomplished writer. Unavoidably, he has lost some of his charisma and urgency since he became another plain old Guardian columnist, with a picture by line.

There is authority in anonymity. Wouldn't you read The Economist differently if it became a conventional line up of faces paraded over opinions? It does not matter much what one journalist thinks, but a newspaper leader immediately assumes the gravity and insight of Plato.

Anonymity is above all associated with authenticity. The controversial lobby system in Parliament is a method for politicians to say what they really think in unattributable briefings. You may argue that politicians should say the same thing in private as they do in public, but it is actually only Boris Johnson who thinks aloud.

Sometimes the truth is too complex or unpalatable. A lame duck Government must proclaim its confidence in winning, even as the water laps around its knees. Similarly, one can only ever talk publicly of victory in Afghanistan, while privately everyone is discussing far more troubled scenarios. When describing colleagues and bosses, the political mind

divides silkily. In public, it pledges support, admiration and unity. In private it concedes that colleagues are insane, incompetent and doomed. This amounts to a balanced view.

Where anonymity is most useful is in supplying information that would otherwise not surface. There is a mostly honourable line of whistleblowers, endowed with a sense of the public interest.

Naturally, a sense of outrage may coincide with self interest and vanity. John Wick, the former SAS officer who handed over the disc of MPs' expenses to the Telegraph, said that he was motivated by politicians' comparatively wretched treatment of the Armed Forces. A good deed is even more appealing when there is a hundred grand in it for you.

When Clive Ponting leaked documents to Tam Dayell revealing that the Belgrano was retreating when it was attacked and sunk by the British during the Falklands War, he did it for more straightforward reasons of personal morality, or perhaps moral grandstanding.

Some whistle-blowers are not equipped for the tempest of public recognition. Who can forget the anxious, academic features of David Kelly, the former UN weapons inspector, frantic with his stomach- curdling knowledge that Alastair Campbell was closing in on him.

For some people, such as Belle de Jour, or political bloggers, public acknowledgement is, at worst, an anticlimax. For David Kelly it tipped him into extreme depression and suicide.

The main advantage of anonymity is that you can express yourself freely and vividly. Compare the formulaic public note-taking of a policeman with the compelling real time blog of Night Jack, or the Random Acts of Reality blog by a paramedic in the London ambulance service. The daily litany of drunks, time- wasters and the dramatically injured, gives an insight into public service in all its splendour and bone-headed bureaucracy.

When Night Jack was identified on the instruction of Justice Eady, as a detective constable with the Lancashire Constabulary, he received a written warning. He was in danger of jeopardising trials as well as forfeiting the camaraderie and trust of colleagues. Justice Eady made a landmark pronouncement that " blogging is essentially a public rather than a private activity".

There is an argument that bloggers or Twitterers or anyone who chooses to be anonymous want it both ways. They want total freedom of speech without accountability or responsibility for what they say. Who can blame them? The spotlight is almost always pernicious, as Cathy Ashton has found. She quoted wistfully the old maxim that you can achieve anything so long as you don't want to take credit for it.

This is the great power of anonymity; it is all message without the contradictory jumble and compromise of human clothing. It is Banksy versus the confusing exhibitionism of the fourth plinth. As a blogger mourning the end of Night Jack wrote: "In the future, everyone will be anonymous for 15 minutes." And, as Belle de Jour has found, once lost, like virginity, it is gone for ever.