An US F15 jet from RAF Lakenheath forced a helicopter into 'evasive action' to avoid a collision, a UK air safety board report has revealed.

The F15 jet was flying in the Llanberis Pass, Wales, when it encountered a Griffin helicopter conducting a mountain flying exercise.

Both aircrafts undertook collision avoidance tactics.

According to the report, the helicopter pilot took immediate evasive action by making a 'hard turn to remain tight against the valley.' The jet pilot 'turned hard right and climbed to increase separation.'

The aircrafts reportedly passed within 400m of one another.

The UK Airprox board report stated that the two pilots 'shared equal responsibility for collision avoidance.

'It was determined that the pilot inadvertently turned north into Llanberis Pass.'

This was the result of a 'navigation error.'

The incident took place on July 5, 2017.