SS, unknown I'm afraid and it opens a whole new discussion doesn't it.
Firstly. No, I have not ever eaten an actual "British" Indian curry. Following the exact instructions on this site, books, ebooks and YouTube, I have eaten BIR curry. Clearly, if people on this site still feel there's still something missing for them, then it is for me as well. If others say they are cooking perfect BIR, then I am as well. What I can say is that there is that same feeling that the commercial aroma and taste is missing here as well, so in that regard I feel the same.
It is worth noting the Amazon blurb for The Curry Secret, which refers to the Indian restaurant recipes being global. I don't believe there is a massive difference between here and there. I've never seen MasalaMark's 3 paste method used and most places have big pots of base gravy and pre-cooked meats and vegies etc. Quite possibly though, true BIR is different. Almost certainly, old school BIR was different to what you have today.
While I really don't see that there can be much difference between the curries here and there, the anecdotal evidence is there to suggest otherwise. Expatriate Brits certainly used to snub Aussie curries, but I'd think that may no longer be the case. The Australian industry was in its infancy 40 years ago but it isn't now.