Consumer organisation Which? said it has received over 150 enquiries from people who believe they have been wrongly accused of pirating copyrighted content.

ACS:Law sends out letters offering to settle the file-sharing accusation in exchange for £500. The company gets its information from internet service providers.

The scheme was run by lawyers Davenport Lyons but was transferred, along with some staff, to ACS:Law last summer.

Which? said it had been contacted by over 150 people, with even more getting in touch after the last wave of letters.

One letter to Which? said: “My 78 year old father yesterday received a letter from ACS law demanding £500 for a porn file he is alleged to have downloaded. He doesn’t even know what file sharing or bittorrent is so has certainly not done this himself or given anyone else permission to use his computer to do such a thing.”

Another said: “I have never been in trouble for anything and I am at my wits’ end. I feel guilty even though I am not.” Matt Bath, technology editor at Which? said innocent people were being threatened for offences they "not only haven't committed but wouldn't know how to commit."

Bath said: "We’d like to see an end to these letters being sent to innocent people and encourage copyright owners to focus their attention on those who are deliberately breaking the law.”

ACS:Law promises to keep sending letters at various points this year - its main wave went out in early January. The firm says on its website: "the fight against internet piracy is winnable, and will we will continue this pursuit into the next decade."

ACS:Law was unavailable to comment at the time of writing. ®