A law firm acting on behalf of games publishers that include Codemasters and Atari against alleged file-sharers is being investigated over claims of bullying and harassment.

The Solicitors Regulation Authority, an industry watchdog, has said that it is investigating a complaint brought against London-based solicitors firm Davenport Lyons by consumer group Which?, The Guardian reported today.

Which? lodged its first official complaint against Davenport Lyons back in 2008, after the firm served notices to 25,000 internet users accusing them of illegal file-sharing.

The letters demanded that people made a payment of £300 in order to avoid court action.

Five games companies - Atari, Codemasters, Reality Pump, Techland and Topware Interactive - were involved in the action, all appointing Davenport Lyons to act on their behalf.

However, Which? branded the letters as "bullying" and "excessive" and said that Davenport Lyons was making incorrect assertions about the nature of copyright infringement and ignoring evidence presented in defence. It added that the letters incorrectly claimed their recipients were legally responsible for ensuring their internet connections were properly secured.

Deborah Prince, the head of legal affairs at Which?, said that she was pleased the SRA had finally taken action on the complaints.

"We're pleased to see some action at last from the SRA and hope the tide is finally turning in favour of consumers. We now want to see some decisive action to stop these bully-boy tactics," she said.

The action comes as the House of Lords prepares to consider the Digital Economy Bill - which could give ministers the power to disconnect alleged file-sharers and let the courts block websites containing substantial amounts of copyrighted material.