The City of London Police has started contacting websites it believes are profiting by breaking copyright laws.
The letters warn the operators of the sites they are breaking UK laws that carry heavy jail sentences.
If site owners do not contact police by 14 June they face further action, the letters say.
In a statement, the City of London Police, said: “These websites are able to operate and profit from advertising on their sites without having licenses or paying the creators and owners of the films, TV programmes, music and publications. Intellectual property crime is a serious offence that is costing the UK economy hundreds of millions of pounds each year.”
In addition, said the statement, the action would help protect UK citizens from the malicious software and other harmful programs that could be found on these sites.
The initiative came out of work done with UK advertisers, the Federation Against Copyright Theft, the British Phonographic Industry (BPI) and the Publishers Association.
It is not known which sites have received the letters – but both are known to be located and run beyond the UK’s borders.
The letters say the National Fraud Intelligence Bureau has become concerned by “websites causing harm to the UK’s creative economy” and this has led to an initiative between government and media industry groups to target “criminal activity linked to websites involved in online copyright infringement”.
The sites are receiving letters because the NFIB has grounds to suspect their operators are infringing copyright, they say, and if the site owners are found guilty of breaking UK copyright laws they could face long jail sentences.
The letters urge site owners to contact the police to stop further offences being committed, adding if contact is not made before 14 June, the sites could face “police action”.
Quite how international co-operation on the issue will proceed is uncertain but the general activities of multi police force coordination does seem to be increasing.