London: A passenger jet came within 300 feet of colliding with an unidentified flying object, an official probe has heard.

Despite an investigation, the UK Airprox Board - which examines reports of near misses - could not explain the ‘blue and yellow’ object which passed under the Airbus 320.

The incident happened on December 2 last year over Baillieston, east of Glasgow Airport, at around 3,500 feet.

The shocked pilot reported the collision risk as ‘high’.

The A320 was descending into Glasgow in clear conditions with the sun behind, when both the plane’s pilots saw an object around 100 yards away.

The board’s report said: “The object passed directly beneath before either of the crew had time to take avoiding action or had ‘really registered it’, although they both agreed that it appeared blue and yellow (or silver) in colour and was “quite large” with a small frontal area.

“The controller stated he was not talking to anyone else in that area and nothing was seen on radar.”

In its report, the board dismissed a variety of possible explanations.

It said: “In the absence of a primary radar return, it was unlikely that the untraced aircraft was a fixed-wing or rotary-wing aircraft or man-carrying balloon.

“It was considered that a meteorological balloon would be radar-significant and unlikely to be released in the area.

“A glider could not be discounted but it was felt unlikely that one would be operating in that area, due to the constrained airspace and the lack of thermal activity due to low temperature.

“Similarly, the board considered that a hang-glider or para-motor would be radar significant and that conditions precluded them.

“Members were unable to reach a conclusion as to a likely candidate for the conflicting aircraft.”