According to “British Civil Aircraft since 1919 vol 2” there was a growing demand between 1946 – 48 for the rapid transport of ship’s crews and spares and the delivery of machinery to the Overseas Food Corporation in East Africa and the carriage of pilgrims to the Near East. Halifaxes played a prominent part in this. The paragraph goes on to list several of the smaller airlines involved but does not mention C.L. Air Surveys. I wouldn’t be surprised if that was the reason for purchasing them though. They were based at Ringway according to the same source.