LONDON (REUTERS) - A "near miss" involving a drone flying just metres from an Airbus A320 at Europe's busiest airport Heathrow has prompted British authorities to issue a warning to drone-users, as worries grow over unmanned aircraft flying near airports.

In another incident, in Poland on Monday, a Lufthansa plane with 108 passengers on board nearly collided with a drone as it approached Warsaw's main airport.

Britain's Civil Aviation Authority warned drone-users of the risks on Wednesday after seven recorded incidents where drones had flown near planes between May 2014 and March 2015 at different UK airports.

The most serious, involving the A320, took place in July last year, when a small black object flew 6m above the aircraft's wing as it came into land at Heathrow, in an incident classed as having a high risk of collision.

"Drone users must understand that when taking to the skies they are entering one of the busiest areas of airspace in the world," said the CAA's director of policy Tim Johnson.

In Britain, doing anything to recklessly endanger an aircraft is a criminal offence, but authorities failed to trace the drone-user in the Heathrow incident.

In response to the incidents and due to the rising number of drone-users, the CAA said it had set up a "dronecode", bringing together existing air safety rules and putting them online to publicise them.

Under the UK's existing Air Navigation Order, drone pilots must keep their craft within sight - effectively no more than 500m away - not fly them higher than 122m, and, if fitted with a camera, must stick to other guidelines when near people, buildings or at events.

With the use of commercial drones for applications from filming to sports events and agriculture booming, the European Union (EU) is currently working on new regulations for drones to protect the safety and privacy of its citizens.

The new EU regulations are due to be presented in the autumn as part of the European Commission's new aviation package.