Hi Martin
I'm sure the boiler is as Mick has said for a "Project" as are the set of frames shown on the right of the picture, the frames etc on the left would appear to be for the G1 "Dee". Both designs are described in books published by the Gauge 1 Association, see http://www.g1mra.com The project design was producedfor the beginner but I think even in the revised books there are still a number of grey areas. The Design is based in the ex SECR class D locomotives, a pretty little locomotive.
Regards,
Bob