There were 23 near misses between aircraft and drones in just six months, according to aviation investigators.
The UK Airprox Board (UKAB) has published reports on the incidents, which took place between April 11 and October 4 last year.
Here is a summary of the 12 which were put in the most serious risk category:
:: April 25
A military Lynx helicopter was forced to conduct an "evasive manoeuvre" to avoid hitting a drone over Hambrook, Gloucestershire.
The pilot said the object passed just one rotor span down the side of the helicopter.
:: June 17
The pilot of an autogyro was on a training flight over Detling, Kent at 1,500 feet when he encountered a drone.
The aircraft missed the drone by around 20 metres and the pilot assessed the risk of collision as 'high'.
:: July 9
Both members of the flight crew on an RJ1 aircraft spotted a drone at an altitude of 4,000 feet over Detling, Kent.
It passed 60 feet below the left wing.
The UKAB concluded that it would have been "impossible" for the drone to have been flown legally because at that height it could not be seen by an observer on the ground.
:: July 26
A silver drone passed within two wing lengths of a BE200 aircraft as it was coming in to land at Southampton Airport.
Investigators found that "chance had played a major part" in a collision being avoided.
:: August 11
A Chinook pilot was carrying out a simulated engine malfunction near RAF Odiham, Hampshire when a quadcopter drone with an attached camera was seen around 75 feet to its side.
:: August 27
The pilot of a Dornier Do328 short-haul jet - which typically has capacity for around 30 passengers - was at 2,800 feet on the approach to Manchester Airport when he spotted a bright blue drone.
The UKAB determined that the drone was not permitted to be within that airspace.
:: September 13
A Boeing 737 suffered a near miss with a drone shortly after taking off from Stansted Airport, Essex.
The incident happened "so quickly" that there was no time to take avoiding action, the pilot said.
:: September 13
In the skies above the Houses of Parliament a drone came within 20 metres of an Embraer 170 jet on its approach to London City.
The UKAB considered that the drone operator was the cause of the near miss.
:: September 22
Shortly after a Boeing 777 had taken off from Heathrow Airport a drone narrowly passed down the right hand side of the airliner.
Investigators concluded that the drone was at the same height and within 25 metres of the jet.
A report was made to police but the drone operator was not traced.
:: September 30
A drone was flown within a few metres of a passenger jet landing at Heathrow.
The pilot of the Airbus A319 stated that the drone may have been just 20 feet (six metres) above and 25 yards (23 metres) to the left when it passed by the aircraft.
The jet was flying at an altitude of 500 feet and was on the final approach to the west London airport when the drone was spotted.
:: October 2
A Dornier Do328 pilot assessed that there was a high risk of collision when a drone passed his left wing by less than 50 feet (15 metres).
The incident occurred at an altitude of 3,000 feet shortly after take off from Manchester Airport.
:: October 4
A PA28 light aircraft pilot was flying over Otherton Airfield, Staffordshire as a drone passed about 20 feet from his wing-tip.