Heathrow airport is launching an investigation after an unemployed man found a USB drive containing sensitive security information on a West London street.

The Sunday Mirror, which first reported the incident, said the man provided the newspaper with the memory stick containing 2.5 gigabytes of unencrypted data, after which the publication informed the airport.

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QEII security revealed

The USB drive contained dozens of folders with maps, security routes, timetables and types of identification need to access certain parts of Europe's busiest airport.

The device also reportedly contained detailed information on security measures taken when Queen Elizabeth II uses the airport.

Heathrow said in a statement that it has robust security measures in place and remains "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," the airport said. "We have also launched an internal investigation to understand how this happened and are taking steps to prevent a similar occurrence in future."

The apparent security lapse comes as Britain is on high alert following a series of terrorism attacks over the past year.

Heathrow airport is the most trafficked air hub in Europe and is considered a target for terrorism attacks.

cw/kl (AFP, AP, dpa)