I have Chevrolet, Ford, Dodge and Fargo listings but for a complete >1944 DOMESTIC theatre listing contact Groucho:
http://www.milweb.net/go/groucho/
The Vauxhall Dunstable Plant was built near the AC-Delco Plant of course (then AC-Sphinx Spark Plug Co Ltd). During the war some associated company, Delco-Reny & Hyatt Ltd, production was moved from the DRH factory in Grosvenor Embankment next to the Victoria railway bridge over the Thames to part of the AC-Sphinx Plant. This was basically tank electrical wiring looms etc. moved by the Ministry (of Supply?) away from the vulnerable Thames-side location to somewhere inland, safe from bombing. DRH used to manufacture electric motors for hanger doors, and Hyatt bearings for the doors! AC-Sphinx produced sparking plugs for the war effort and contact-breakers, etc.
After the war negotiations started in earnest in 1948 to allow General Motors Ltd to build a dedicated truck plant as Luton did not have the capacity to expand. They forced the exchange control comittee's hands and GM invested £25 million in dollars in the end to acquire more land next to that bought in 1938.