Britain’s Heathrow airport has launched an internal investigation after a USB drive containing security information including security measures  to protect the Queen was found on a London street.

The Sunday Mirror reported a member of the public found the USB drive and turned it over to the newspaper.

The device contained 76 folders, including information on how to access restricted areas. The data wasn’t encrypted.

Heathrow released a statement saying security plans have been reviewed in light of the incident and the airport remains “vigilant to evolving threats by updating our procedures on a daily basis”.

The airport says security officials “launched an internal investigation to understand how this happened and are taking steps to prevent a similar occurrence in future”.

Some of the files on the USB drive reportedly disclosed the types of ID needed to access restricted areas, a timetable of security patrols and maps pinpointing CCTV cameras.

One document highlighted recent terror attacks and talked about the type of threat the airport could face, the newspaper report said.

The Heathrow statement said the airport’s “top priority” was the safety and security of passengers and staff.

“The UK and Heathrow have some of the most robust aviation security measures in the world, and we remain vigilant to evolving threats by updating our procedures on a daily basis.”

Heathrow, located 23km west of London, is the second busiest international airport in the world. Last year the hub handled a 75.7 million passengers.

Security at the airport is handled by the aviation security unit of London’s Metropolitan Police, although the army has been deployed at the during periods of heightened security.

– With AAP