None of this really matters - it's a BBC article written for British audiences in British English. The goal is to communicate with the audience. I think the only clear term for British people would be "Katsu Curry Sauce", or perhaps "Katsu Sauce".

I guess they can do that as a matter of fact, but then this is going to continue until they quit, along all those weird beef Brits have with Japanese food and culture in general - they have multiple for inexplicable reasons.