Maverick French lawyer Jacques Verges says he will file a suit against the UK at the international war crimes court over the abuse of Iraqi detainees.
Verges has defended many notorious clients
Mr Verges told French news agency AFP that the suit would be on behalf of "the families of prisoners".
A spokeswoman for the International Criminal Court in The Hague told BBC News Online it did not comment on complaints filed by individuals.
Mr Verges says he has been asked to defend former President Saddam Hussein.
"The reality of torture and systematic abuses of the dignity of Iraqi prisoners, sometimes followed by murders, both by US and British troops is no longer in question," the text of the complaint reads, AFP reports.
"There are strong presumptions that the facts that form the basis of our complaint were committed with the participation of nationals of the United Kingdom, which unlike the US... is a party to the [Court's] statute," it said.
The US is not a party to the statute and has signed bilateral agreements with several countries to exempt its citizens from the ICC jurisdiction.
ICC spokeswoman Claudia Perdomo told BBC News Online the office of the prosecutor did not comment on communications it received - so far the number is nearly 800.
It can start an investigation, but as a court of last instance, it only takes over cases which a state party has failed or is unable to investigate, Ms Perdomo said.
In his long career, Jacques Verges has acted for Nazi war criminal Klaus Barbie and for Carlos the Jackal, and says he has represented former Yugoslav leader Slobodan Milosevic.
Mr Verges, 79, is said to have been a friend of Pol Pot, the Khmer Rouge leader behind Cambodia's genocide.
His controversial career has earned him the nickname "the Devil's advocate".