Two US fighter planes were in danger of colliding with a pair of skydivers in Cambridgeshire after the jets inadvertently flew across a parachuting site, a report has revealed.

A GoPro camera fitted to the helmet of one of the parachutists recorded video of the F-15 fighter jets flying beneath them as they fell at 120mph.

The UK Airprox board, which reports on air proximity events in British airspace, said regulations and procedures were not complied with, and that although the pilots should have been made aware of the skydiving centres as part of their normal briefing routine, they ought to have either questioned air traffic control or avoided the area.

As they were handed over from air traffic controllers at RAF Coningsby in Lincolnshire to those at RAF Lakenheath in Suffolk just before 1.20pm on 17 April this year, the planes slightly changed course to avoid a refuelling tanker. After the changeover the frequency became busy, meaning the controller was unable to change the heading of the F-15s.

“The controller believed he would have plenty of time to change the heading of the F-15s when they came on frequency,” the report said. “However, the frequency became busy just as they transferred and so by the time the F-15 pilots checked in with the controller they were already about to fly over Chatteris.”

The incident was classified in the second-highest danger category but the board was unable to establish how close the two pairs came to colliding. The pilots did not see the parachutists, the report said.

The board noted it was “unfortunate” that the air traffic controller at Lakenheath had not warned the pilots “due to the completion of the handover at a busy time”. The controller had not subsequently filed a report on the incident.

A US air force representative had recently retired at short notice, leading to a gap in the advisory post during which time a report related to the incident was overlooked, the report said.

“A full-time liaison officer had been recruited and was due to be in post in the coming months; in the meantime, the post was being covered by other personnel,” the board reported. “Despite the lack of report, he was able to provide the board with details about the circumstances.”

The US air force command at Lakenheath has rebriefed all of its crews to remind them of the need to avoid the parachuting site.

Operators from Chatteris, home to several skydiving centres, call Lakenheath each morning to advise that they are active, and the board said there was “very little more that Chatteris could have done from an operational perspective to prevent the [air proximity event]”.

The parachutists, who had reported the event before Airprox contacted the pilots of the US planes, had “no control over their speed or direction while in freefall” but could have opened their parachutes to slow their descent, the report said.