Resurrecting this after a year - bought a very similar one and managed to bring it back to life last week. Slightly different pipework than pictured underneath the instrument panel, and a different design of the pump trailer, probably a bit later one. The pump still shows a FSM serial number though.
Must investigate if the factory records are somehow still preserved. I assume if the factory was bought by Jaguar Cars, it might be part of some kind of a heritage collection.