Austin Welfarer HCG 153.

This picture is of another Welfarer at the old Farnborough Station (circa 1953), which shows HCG 153 (registration issued between April 1949 and Sept 1950), that would have entered service a little later than HAA 701.
I do believe Gordon Adams (formerly Chief Ambulance Officer, Hampshire) joined around 1953 and, that being the case, would probably have driven this vehicle.
Thanks to Ron Lilly for the picture and information.