Heh, its the same thing here as well for Japanese food. Being something of a japanophile myself, I can detect the clear differences between the regular Chinese/Korean owned Japanese style restaurants and authentic Japanese ones. The latter are quite rare and normally quite expensive. I'm not dissing the non-authentic ones....they are just not so accurate and more "mainstream" in their dishes....and there are often outright Chinese selections on the menu too.
Real japanese food for example is not meant to be dipped in tons of soy sauce and fake wasabi...which I see most people doing at the mainstream joints...esp the "all you can eat" ones. It's meant to be eaten cleanly, it should be of that quality to get the nuances of the ingredients. This is true even for more regular "Udon" style eateries. In Canada, the West coast has some really good more true Japanese restaurants, with places handed down through generations of Japanese immigrants.
But then if you dont want to break your budget and compromise, the mainstream ones offer the best value by far....you just have to have been to the authentic versions a few times at least to create something of a "reference" so you know which of the "riffraff" are closer to the real thing and which items are the best bet etc...I would imagine its tough in the UK since there is no real history of major Japanese immigration like West Coast North America. The one I want to try yet is the cuisine of the Japanese people in Brazil....to see what they have retained and what they have merged/fused/adapted etc.
@Nihonjin1051 can probably explain more and better. Actually going to Japan for the first time was quite an eye-opener to me to how the Japanese value their core cuisine....and what quality they expect.
This was also a really great watch to get a perspective on the subject: Jiro Dreams of Sushi (2011) - IMDb
LOL!! If you're referrIng to these so called Japanse sushi buffets here in the US? Sure, most of them are usually owned by Korean or Chinese. There's a good one close to my place; the owners are Taiwanese in fact. The owner speaks some Japanese so that's why I frequent his business. :]