The London-based lawyer at the heart of a huge row over internet piracy, Andrew Crossley, breached the solicitors code of conduct with his method of accusing people of illegal filesharing, a judge has ruled.

ACS:Law, the law firm created by Crossley, sent tens of thousands of letters demanding "settlement" payments of about £500 from people it accused of illegal downloading.

The firm apparently recouped hundreds of thousands of pounds from the controversial "speculative invoicing" scheme before it finally brought 27 cases to court earlier this year. However, Crossley tried to halt the trial before he had to bring any evidence.

Ruling in the Patents County Court in London on Monday, Judge Birss QC described ACS:Law's pursuit of illegal filesharers as "amateurish and slipshod" and said it had "brought the legal profession into disrepute".

Birss said Crossley had breached the solicitors code of conduct because he was responsible for the licence agreement between Media CAT and the original copyright holders, and stood to profit from it. The code of conduct states that "you must not enter into an arrangement to receive a contingency fee for work done in prosecuting or defending any contentious proceedings" before the court.