Much of the serial was filmed on location in Aldbourne, Wiltshire. The location shoot was awarded two weeks' filming, more than double the usual amount at the time, leading to a lot of the finished story being set outside, rather than in studio. Membury airfield in Berkshire and Bridge Farm, Ramsbury, were also used briefly as locations. Filming began on 19 April 1971 and saw pleasant, sunny weather for the first week, leading to sudden overnight snow in the second week – causing filming to be delayed. Some episode one scenes were filmed at night – a rarity for the show, although some of these scenes were filmed during daylight with a dark filter put over the camera lens. Other dark indoor scenes were filmed in a disused aircraft hangar at Bridge Farm, Ramsbury. Filming for the serial caused great excitement in Aldbourne, with a lot of the village residents appearing as extras, as well as the Headington Quarry Morris dancers performing a routine in episode four.