Roger Pearson looks at how Westminster council turned to the Environmental Protection Act in its attempt to stop "carders'.

Westminster City Council is trying to get rid of prostitutes' cards that are "fly-pitched" in telephone kiosks. Unfortunately for the council it is coming up against more legal obstacles than it expected in its fight to crack down on the problem.

Solicitor, Brian McDonnell, of specialist criminal practice Claude Hornby & Cox, has become the "carders" champion – the nickname for the men and women who place cards in phone boxes. They are said to earn up to £100 a day by their activities.

When Westminster Council prosecuted carders on the basis that they were causing criminal damage to the phone boxes, McDonnell successfully countered that line of attack. He had equal success in defending a carder whose cards were branded an "indecent display".

More recently, the council turned to the litter laws in a bid to curb the carders. But the carder involved beat a trail to McDonnell's door, who demolished that line of attack as well.

At first it looked as if the council had found the answer. Carder, Henry Felix, 43, a veteran of some 50 court appearances for carding and who has been fined thousands of pounds over the years, was convicted by Marylebone Magistrates, under the provisions of the Environmental Protection Act 1990, of "littering" a phone kiosk in London's Edgware Road with adverts for the services of call girls.

That conviction, along with fines and legal costs totalling £320, was upheld when Felix appealed to Knightsbridge Crown Court. But in the High Court, Lord Justice Kennedy and Mr Justice Blofeld quashed the conviction.

In a crucial decision in respect of the legal definition of telephone kiosks, the High Court ruled that modern BT phone boxes, which are enclosed on three sides with a roof and a door and a gap at the bottom, cannot be defined as a "public open space".

Mr Justice Blofeld said the fact that there was a gap of some six inches at the bottom of the boxes did not turn them into an "open space" in the eyes of the law and in those circumstances Felix could not be convicted of causing litter in a public place.

For McDonnell, the increasing role as an expert in the law relating to carding was won more by accident than design. It was hardly surprising given the geographical location of the firm in London's Soho that, when a carder was looking to be defended several years ago, he should turn to Claude Hornby & Cox.

When it happened, McDonnell, who was a trainee at the time, was handed what was generally considered to be a run-of-the-mill case. He says: "I formed the opinion that the whole subject raised some very interesting law, of which some points should be tested in court.

"Carders have been a thorn in the side of the authorities for some time. Councils have tried, creatively, to prosecute these people under a lot of different statutes. But in doing so they have been using the law for means for which it was really never designed.

"I think that building case law in this field serves as a warning that the use of inappropriate laws in a bid to combat problems that they were never specifically designed to combat can prove ineffective and a waste of both time and legal costs."