Newly-released files show a series of drone incidents near UK military bases triggered official investigations.

Ministry of Defence (MoD) officials probed cases which included a pilot reporting an unmanned aerial vehicle (UAV) at 20,000ft.

Another drone, said to be a quadcopter, which was said to have ‘hovered over barracks’.

According to reports, the UAVs were also recorded as coming within close proximity of military facilities, according to the information released by the MoD’s Directorate of Security & Resilience.

One was sighted over the roof of a building while another landed on an ‘upper roofed area’.

There were a total of 21 incidents between January 2022 and February this year, said the Metro newspaper, which filed a Freedom of Information request.

On one occasion a security team was recorded as having located the operator. The incident report reads: ‘Report of drone flying.

‘Officers conducted area search, operator located. Spoken to by officers, who viewed footage from drone, operator voluntarily deleted all footage.’

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Only one of the other reports, where a drone was being used at a pre-planned event, shows any sign of the operators having been located.

Two other incidents concerned an object described as a ‘drone/microlight glider’ which was seen by ‘multiple witnesses’ in one case.

Another report in the list of incidents states: ‘A drone (believed to be a quadcopter) hovered over barracks.’

Area searches were carried out in seven cases but no evidence of UAV activity was found.

The log in another of the incidents states: ‘Report from pilot of drone at 20,000 feet. Nothing seen from the ground, area search carried out for operator, no trace.’

The Metro reported that a military facility’s own systems detected a UAV in one case. The log reads: ‘Drone system activated, showing drone. Officers attended, no trace.’

The information has been revealed at a time of heightened international concern about aerial spying by foreign powers.