A pilot flying in south Hertfordshire had a dangerous encounter with an unknown object, new data revealed, as concerns grow over spy balloons.

The captain and co-pilot of an Airbus A320 noticed an object which was “grey/silver in colour and about the size of a large drone or balloon”, while travelling near Hatfield on July 16 last year.

The incident was included in UK Airprox Board (UKAB) data, analysed by PA news agency, and comes after the UK government said it will do “whatever it takes” to keep the UK safe from spy balloons.

The airliner’s pilot described the object as “almost shiny in appearance” and said it passed “within 100-200ft below their aircraft”.

The UKAB concluded the incident had the second-highest level of risk as “safety had been much reduced below the norm”.

More reported incidents 

Another incident revealed in the data was on December 17, at 1,850ft above Enfield in north London, where the pilot of an EV97 light aircraft reported an object that “could have been a balloon or an egg-shaped drone” flying “directly below them by 50-200ft”.

An air traffic controller told the board on September 25 a pilot in the cockpit of an Airbus A319 airliner was “distracted” by an object which was “either a balloon or a drone” passing along the side of the plane.

The pilot said it was in “close proximity” and described it as a “white object, considered to be a threat” and “rectangular”.

Four days later, a pilot on a Boeing 737 taking off from Stansted Airport, Essex, reported seeing “a glinting object” as near as 50 metres away.

Get a Watford Observer digital subscription for just £1

Watford Observer: Stock plane image.Stock plane image. (Image: Pixabay)

The pilot “first thought it was a balloon”, but then believed that was unlikely given it was at an altitude of 9,000 feet, so believed it was a drone.

On July 2, a pilot of a Boeing 757 saw “what was first thought to be balloons” at 7,500ft shortly after departing from Manchester Airport.

The report went on to state that “as the black object passed down the right-hand side it looked like a drone”.

In October 2017, the Met Office said it “launches over 4,300 balloons every year from six locations across the UK” and is “involved in launching thousands more around the globe”.