An investigation has been launched at Heathrow Airport after a memory stick reportedly containing confidential security information was found in the street.

The Sunday Mirror says the USB stick - which was not encrypted and had 2.5GB of data - was discovered by a member of the public in Ilbert Street in Queen's Park, west London, and handed to the paper.

It reportedly contained files revealing information such as security measures used to protect the Queen at the airport, the types of ID needed to access restricted areas and the locations of CCTV cameras and tunnels linked to the Heathrow Express.

A spokeswoman for the airport said security plans had been reviewed in light of the incident:

Heathrow's top priority is the safety and security of our passengers and colleagues.

Heathrow spokeswoman