Heathrow Airport has launched an internal investigation after a man found a USB containing security information on a street in west London.
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The USB stick has 76 folders containing maps, documents and videos, which include details of the Queen's route to the airport and security measures it used to protect the monarch, the Sunday Mirror reports.
It also has files revealing the types of ID required to access restricted areas of the airport, timetables of patrols used to guard the site and maps pinpointing CCTV cameras.
Police fear the files may have been hacked and downloaded to the memory stick. But as it was found close to the airport, it is also likely that an airport worker accessed the data and lost the USB.
In a statement, Heathrow Airport said: "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.
"We have reviewed all of our security plans and are confident that Heathrow remains secure.