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 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.

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. 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 online I would will him on. He blogged because he had something vital to say.

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’s leading article 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.

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.

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 Daily 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 whistleblowers 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.

It is all message without the contradictory jumble and compromise of human clothing.

And, as Belle de Jour has found, once lost, like virginity, it is gone for ever.