Two planes almost crashed into each other over London this summer, according to a report by the Air Accidents Investigation Branch.

A serious incident was narrowly avoided as a Turkish Airlines Boeing 777 carrying 232 people and a Citation 525 jet, carrying two pilots and a single passenger, were both flying at around 4,000 feet.

The report claims that as the Turkish Airlines plane was heading to Heathrow, the Citation was just half-a-mile away. The incident occurred because of a 'readback' mistake which went unnoticed by the London City Airport control tower. Apparently, the private jet was cleared to climb to a height of 3,000 feet, but when the pilot confirmed the instruction he said he would be proceeding to 4,000 feet.

The Citation was only half a mile away from the Turkish Airlines Boeing 777 and between 100 and 200 feet below it when its pilot realised the danger and managed to take last minute action to avoid a collision.

The captain of the Citation claimed in his report that he had a constant visual of the passenger plane. According to the AAIB, if the weather had been bad the only thing to prevent a disaster in such situations is on-board collision-avoidance systems and has recommended that all planes flying over London should be required to have collision-avoidance systems on board.