Two decades on, the back wall of nearly all boxes in the central area of the city is an eye-snagging patchwork of explicit cards selling sex. Although the use of cards has spread to a few seaside resorts outside London, it is in the capital that most people come into contact with this peculiarly localised form of advertising.

Current estimates are that more than 13 million vice cards are deposited in phone boxes in central London each year, which amounts to 36,500 a day – and that there are only around 250 prostitutes behind this monsoon of paper. Both the Government and London's local authorities are keen to rid the city of this highly visible sign of a thriving sex industry. The fundamental objection to the adverts is that they stimulate a trade that is marked by drugs, illegal immigration, people trafficking and under-age sex, but there is also the problem of their negative impact on how tourists view the capital, their potential influence on young people and the problem they create with litter.

Prostitutes are very reliant on the cards: although prostitution and advertising prostitution are not illegal in the UK, soliciting for business on the street is, so phone box adverts offer a cheap and convenient way of staying inside the law. And attempts since the 1980s to prosecute carders under environmental or criminal damage laws have mainly failed. Even a piece of legislation that in 2001 specifically made the placing of cards in a phone box a criminal offence only temporarily reduced the flow – the increase of the average day rate for carding to £200 was obviously proving adequate compensation for taking an increased risk.

Removal and prosecutions

Local authorities and the police are only able to prosecute carders they happen to catch in the act, and with more than 700 phone boxes in central London, constant monitoring of the phone boxes is simply not financially viable. The other line of attack is removing the cards: BT (the owner of most of London's phone boxes) and councils both run continuous cleaning programmes – BT alone takes down 150,000 cards a week – and the police periodically raid addresses and confiscate supplies.

Alongside its cleaning programme, BT also operates a policy of blocking calls to numbers that are repeatedly used on phone box adverts, but in the last decade this has meant that the majority of women have switched to using mobiles. The mobile companies have continued to avoid taking a position on vice numbers, despite campaigns such as that run by Tory councillor Kit Malthouse, who in 2005 printed up 20,000 mock prostitute cards printed with the names and business addresses of the CEOs of the major mobile phone companies, and gave them out to shoppers on London's Oxford Street.

Independent studies have shown that call barring is the most effective way of reducing carding. But the English Collective of Prostitutes says it will sue for restriction of trade if all telephone companies agree to block calls. It argues that this is really a question of safety, that without phone lines women are unable to work from premises, and are therefore forced back onto the street, an environment in which they are far more exposed to violence.

The International Union of Sex Workers recently suggested an old solution to the problem of indiscreet advertising: the publishing of a directory of London's sexual services – something that was first done in the form of (the phenomenally successful) Harris's List Of Covent Garden Ladies in 1757.