Thank you both for this information! Those images are fantastic and, I think, explain something I had previously missed. This being that airframes were made complete at the factory then broken down again for transportation to the airfield for final assembly. Those DH9 on the lorries have no engines! I had previously wondered why that DH9a was photographed without an engine.
The conclusion being my DH9a was the first or last one before leaving the maker. Or the first or last one on arrival at final assembly just before being fitted out?
I had previously thought the hangar was at Westlands. However the serial number info (thanks) would suggest either Airco (Hendon) or Wearing & Gillow (Hammersmith / Acton).
Another question then. Were Airco airframes made and fitted out on one site (Hendon)?