The only similarity between UK stock cars and US sprint cars is the four wheels and a roof mounted wing.
Electric stock cars are 1/12th scale and race indoors on carpet. They have a solid rear axle with no diff, and have a one piece chassis that includes front and rear bumpers and side guards. The racing is a contact sport, so you need the bumpers to protect the chassis when the car behind decides to help you out of the way when they pass. A 1/12th stock car looks like this
http://www.mardavespares.com/mardave...-v12-f2-rc-kit
Nitro 1/8th scale stock cars are powered by a .21ci engine and race on asphalt oval tracks. They have a single direct belt drive to again a solid rear axle with no diff. Rear suspension is a single trailing arm on each side. Chassis are usually scratch built from welded steel to withstand the impacts from the full contact racing. The cars look like this
http://www.ovalnet.org.uk/gallery/16...g-weekend/307/