Bristol Cars was formed when the Bristol Aircraft Company joined forces with Frazer-Nash’s parent company, AFN. Before the War, AFN was the concessionaire for BMW in the UK, so after Bristol took possession of BMW’s designs, AFN was the natural choice for a build partner. The 400 was the first fruit of their efforts, and was clearly based on a mixture of the pre-war BMW 326 (chassis) and 327/80 (body). Many changes were made – and aircraft levels of build quality were a clear benefit.
info from Octane