Clive,
I am not sure that is right. I thought there was a strong connection with BMC / British Motor Holdings, then British Leyland. Looking at Graces Guide and their timeline, seems I was correct http://www.gracesguide.co.uk/Pressed_Steel_Co They continued with BL then when the Mini production was set up by BMW, they were drawn into that group, now called Swindon Pressings.
They did have a plant at Linwood in Scotland next to the Rootes plant and made the Imp bodies there