A US fighter jet came within 500ft of a civilian plane over Norfolk having 'not fully assimilated' information from air traffic control, a safety report has found.

An Airprox report concluded two F15s from USAF Lakenheath had 'inadvertently flown into conflict' with the Beechcraft Super King Air (B350), over Marham on November 6 last year.

The Airprox board investigating the conflict noted the F15s were given incorrect traffic information just prior to the closest point of approach. The inaccuracy of the late traffic information was said to have been 'likely to have compounded the problem' as the F15 pilots manoeuvred north-east, inadvertently towards the B350, while thinking the conflicting traffic was to their west.

One of the jets was said to have come within 500ft of the B350.

At the time of the incident, it was noted that the air traffic controllers from RAF Swanwick in Hampshire were said to have been 'extremely busy'.

Other factors outlined in the report include the B350 being asked to change frequency just prior to the incident, and it being on an a different frequency to the F15s.

In conclusion, the report stated: 'After much discussion, the board ultimately agreed that the cause of the Airprox was that the F15 pilots had inadvertently flown into conflict with the B350 having not fully assimilated earlier traffic information.'

The erroneous traffic information just prior to the incident was considered to be only a 'contributory factor' because they had already started their turn towards the B350 before the call had been made.

One of the air traffic controllers was reported to have perceived the severity of the incident as 'high'.

However, the board considered that although safety had been 'degraded', the actions of F15 pilots had prevented a risk of a collision therefore assessed the Airprox as risk Category C - no risk.

After an investigation at RAF Swanwick, the incident has been used as an example of both the importance of prioritising timely traffic information and effecting tactical airspace management.

A USAF spokesman said: 'We are confident the risk of Airprox events is minimized by our continuous training, consistent focus on flight safety and our direct communication with Royal Air Force and civilian air traffic control services.'

An RAF spokesman said 'there was no risk of a collision during this minor incident'.