The occasion was Brooklands Easter meeting in 1937, the car was MG NE Reg Number JB 4607 and was being driven I think by FW Carr who bought it from new and had the supercharger fitted. This NE is now owned by Pete Thelander in the USA and is still raced but in un-supercharged form. I may have some photos of this car I took at Laguna Seca in 2005 if you are interested in seing them.