Mobile phone company O2 has waded into the row over controversial letters sent by lawyers to alleged internet file-sharers.

O2 broadband customers are among the thousands who have received letters from London firm ACS Law, which acts on behalf of DigiProtect, an anti-piracy firm, and clients whose copyright in music, software, computer games and films has allegedly been infringed by illegal file-sharers.

An O2 spokeswoman said: ‘We do not support attempts by rights holders and their lawyers to bully or threaten our customers about file sharing. Nevertheless, where we are legally obliged to provide information and a court order is presented, we will comply with the law.’

Andrew Crossley, principal at ACS Law, denied that the letters were bullying or threatening. He said the firm sends out letters of claim to people whose internet accounts have been identified as being used for illegal file-sharing, asking them to respond.

To avoid the matter going to court, Crossley said the firm invites those contacted to enter into a compromise agreement where the matter is settled, typically for around £500. He said responses are considered on a case-by-case basis.

‘We think our practices and procedures are SRA-compliant and based on accurate and compelling evidence that infringement has taken place,’ he said.

Crossley added: ‘We don’t bully anyone, but act robustly on behalf of our clients who are losing vast sums of money through illegal file-sharing.’

Many of the cases being dealt with by ACS Law have been passed on from London firm Davenport Lyons, which has been the subject of an SRA investigation and had two of its solicitors referred to the SDT in relation to letters sent to alleged file-sharers. The two solicitors’ legal representative has rejected the complaints, made by consumer group Which?.

ACS Law is also being investigated by the SRA following complaints over the way it deals with such copyright infringement cases.