A drone almost collided with a passenger plane carrying 165 people as it passed over the Shard in July.
A report from the UK Airprox Board, which records near-misses in the air, said the Airbus A320 was en route to Heathrow Airport on 17 July when its crew spotted a black drone out of their right window.
Crew members estimated it was just 20 metres away from the plane and suggested the drone, which was which was 50cm (20 inch) across, passed over the wing of the plane while it was at 4,900ft - with the pilot saying there was a "high" chance the drone could have collided with it.
Near-misses with drones are increasingly common - with some experts warning the situation is becoming increasingly precarious.
Last July the Civil Aviation Authority urged drone owners to be careful with their toys, after another near-miss with an A320 which brought a drone six metres from its wing over Heathrow Airport.
“We want to embrace and enable the innovation that arises from the development of drone technology, but we must ensure that this is done safely, with all airspace users in mind. It is imperative that people observe the rules when operating a drone," said the CAA's policy director Tim Johnson.
The report on the incident this July pointed out that there are no maximum height regulations for operators of drones which weigh less than 7kg - but it added: "Members agreed the incident appeared to be a very near-miss and that the drone operator should not have been flying in that location at that altitude".