The Bristol Britannia took off from London at 10:10 for a test flight regarding the renewal of its Certificate of Airworthiness. After performing the necessary test, the crew requested a descent from 12000 feet to 3000 feet. Some 3 minutes after starting the descent, the aircraft struck the ground which was obscured by fog. PROBABLE CAUSE: “The accident was the result of the aircraft being flown into ground obscured by fog. This was caused by a failure on the part of both the captain and the first officer to establish the altitude of the aircraft before and during the final descent. The responsability for the accident must rest with the captain. The height presentation afforded by the type of three-pointer altimeter fitted to the subject aircraft was such that a higher degree of attention was required to interpret it accurately than is desirable in so vital an instrument. This, when taken into conjunction with the nature of the flight on which the aircraft was engaged was a contributory factor.”