Aerotel sued a number of companies, including Wavecrest, alleging that they infringed the patent, which dates from 1985 and has expired.

The patent (number 2,171,877) relates to a method of making pre-paid telephone calls that is available for use from any telephone, and to hardware for doing so.

In a ruling dated May 23, His Honour Judge Fysh (sitting as a High Court judge) found the patent invalid on the grounds of obviousness - based on a study of the prior art - and excluded matter under Article 52 of the European Patent Convention.

However, he added that if the patent were in fact valid, it would be infringed.

In a previous case, the same patent had been asserted against Telco Holdings. In that litigation, the first instance judge granted summary judgment on the grounds that the patent claimed a method of doing business. In 2007, despite the parties having settled the case, the Court of Appeal overturned this decision and restored the patent.

However, the courts in that case were not called on to consider the same volume of evidence, and in particular the state of the art at the priority date.

Aerotel was represented by barristers Henry Carr QC and Andrew Lykiardopoulos and law firm Powell Gilbert. Wavecrest and the other defendants were represented by barristers Iain Purvis QC and Kathryn Pickard and law firm Mayer Brown.