The microwave gristle cheese burger certainly continued past BR into the Great Western, First Great Western and then First Greater Western era's, IIRC it must have been around '08 to '10 that it died to be limited only to the then travelling chef services, which suffered immensely from crew availability or the wrong type of train. I can't remember GNER or NXEC ever suffering from lack of chefs the extent the GW franchises did.
Annual co-payments by ÖBB to the caterer for RailJet services are low double digits apparently on catering turnover of around €14m... to quote a statement made by the head of ÖBB "Die Verpflegung im Zug ist Teil des Reiseerlebnisses" or in English "Catering on the train is part of the travel experience.", does a potential 50% subsidy sound reasonable for a UK TOC to cover?
https://www.diepresse.com/5351386/obb-teuer-erkauftes-essen-auf-radern
There are services particularly and ironically enough the GWR Pullman that demostrate on train catering can be very good for that matter the VT and LNER complementary first offers serve perfectly decent food, before that the GNER paid for restaurant service was good, none of these are known to make a profit for the operator and exist or existed as services to increase yield indirectly.
However in all seriousness is there a railway operator in Europe that actually makes a profit on catering provision? DB don't, SNCF don't, OBB don't. RENFE don't publish numbers so who knows. Trenitalia publish that they had catering costs of €90m but not what the revenue was but do also note costs have increased, I'd expect this is code for not a profit making service.