RAF student and tutor pilots flew in formation within 100ft of a glider while practising an emergency manoeuvre almost directly above the East Coast Main Line.

Air safety bosses said as the planes converged near RAF Linton-on-Ouse, North Yorkshire - the busiest military training airfield in the UK - the RAF pilots did not see the glider until it was too late to take avoiding action.

The glider pilot did not spot the two two-seater Tucano turboprop planes until they were below him.

A report to the UK Airprox Board, which examines mid-air near misses, states the RAF pilots had been descending from 9,000ft to 2,000ft south of Thirsk as part of a close-formation recovery at 3.16pm on June 3 when the rear cockpit flying instructor saw the glider to his right.

It was initially tracking parallel to the Tucanos, which have a maximum speed of 340mph, which were about 100ft below the glider.

The Tucanos, returning to No 1 Flying Training School, at RAF Linton-on-Ouse, where Prince William undertook fastjet flying training in 2008, while the pilot of the 260kg ASW20 glider had been using columns of rising hot air to gain height when he heard the Tucano engines below him.

The report states a RAF Linton on Ouse air traffic controller report said its radar did not pick up the glider, probably due to it being above the Tucanos, within the radar antennae's "cone of silence".

Investigators found both aircraft were entitled to be in the area, but all the pilots shared an equal responsibility for collision avoidance and not to operate in such proximity to other aircraft and create a collision hazard.

The report stated: "It is pleasing to see that the glider pilot was listening out on his radio. The board considered that it was unfortunate that he had not contacted Linton on a radio transmitter (RT).

"A military member stated that thermaling above the busiest military flying training airfield in the UK without contacting them presented a serious risk to operations that could have been effectively mitigated by making contact.

"Gliding members pointed out that many glider pilots did not possess an RT licence and so were not legally allowed to communicate on the radio."

"The Board considered the cause and agreed that, in this circumstance, the Airprox was due to the

late sighting by the Tucano pilot and, because he did not see any Tucano until after the closest point of approach, effectively a non-sighting by the glider pilot."

The near-miss follows an incident between two RAF planes near the base last November which led to changes to its air traffic control policy.