Confidential police information about undercover officers and key witnesses in a massive drugs operation was found dumped in a bin.
The highly sensitive files reveal how Merseyside Police watched criminals from an international gang organise lorry loads of drugs into the UK.
The Liverpool Echo reported the revelations that related to the force's Operation Montrose - which eventually led to police seizing £17 million of drugs, £300,000 in cash and the jailing of nine men.
Today, HM Courts Service said an investigation would be launched to establish how the documents came to be dumped at Farringdon Moss recycling centre near Preston.
A spokesman said: "HMCS takes data security extremely seriously and we will investigate all allegations of breaches or incidents."
It is believed a builder discovered the files, which run into hundreds of pages, the Echo reported.