Grace's Guide is my usual first call on subjects like this - there are two vague references to them being 'general engineers' in the 1937 The Aeroplane Directory of the Aviation and Allied Industries (a link which eventually just redirects back to the main entry for the company) and when they merged with RH Wilson in 1958. There's also a Dun & Bradstreet listing from 1961 which says they manufactured aircraft parts.
So I suspect that if they did any work for RR it was probably for the aviation side - possibly classified at the time and/or as a shadow factory? In time of war there would be less demand for new sporting guns - and much high-tech industry was in any case directed into war work whether they wanted to or not!
I hadn't realised that they were an early agent for Hispano-Suiza cars either!