The pilot of the jet airliner "expressed his surprise" after spotting the object shortly after take-off, the UK Airprox Board (UKAB) said.
See also: Europe to urgently assess risk of drones hitting planes
See also: Pilots report several near-misses at UK airports in just one month
He was carrying out a right turn at an altitude of 1,500 feet - a "critical phase of flight" - when the incident occurred.
The report stated that the drone was "extremely close to the aircraft", passing just 50 feet above and 100 feet to the left.
Experts "quickly agreed that there had been a definite risk of collision" and the incident was put in the most serious risk category.
The latest monthly UKAB meeting examined a total of six near misses between drones and aircraft, including reports from near Heathrow, Glasgow and Newcastle airports.
The British Airline Pilots Association has warned that the risk of collision between an aircraft and drones is "unacceptably high".
Last month a drone was believed to have hit a British Airways flight landing at Heathrow, although it later emerged it may have been a plastic bag.
Drone operators must keep their craft away from aircraft and airfields, and not fly above 400 feet.
They are also barred from flying drones with cameras within 50 metres of people, vehicles or buildings, or over congested areas or large gatherings such as concerts and sports events.
In the Queen's Speech it was announced that the Government will introduce new regulations on drones in a Modern Transport Bill.