When I was in London two weeks ago, I saw a lot of "Yo! Sushi" adverts. One of them asked "are you a Sushi virgin?", featuring two smiling Japanese girls in a "kosupure" costume.
The culture of Sushi has spread to the world, and lots of mutations in the memes have taken place. Some of them go beyond your wildest expectations. When I was in a Sushi restaurant in Brasilia some 15 years ago, I was intrigued to find that the sushi was cut into half their usual sizes. Presumably the delicacies would look like canapes and easier to handle and eat then.
Diffusion is a good thing. New possibilities can only be found in variations and subsequent selection process. Having said that, I, as a proud Tokyo resident, can testify that the (in my view) genuine form of Sushi eating can only be found in Japan, or more specifically, in Tokyo.
London's "Yo! Sushi" type restaurants which serve sushi on moving conveyor belts are surely abundant in Tokyo. Families love them. However, a genuine Sushi restaurant can be distinguished by the makeup of the counter. It needs to be constructed with a single plain wood, with the annual ring traces aligned in parallel ("masame"). A piece of wood in such a condition, which is long enough to be made into the counter is rare and highly prized. If you have a chat with the Sushi chef over the counter, he will tell you how much it had cost him to have that particular wood.
You should know that the counter wood is the most important element of a sushi restaurant. Now you have climbed one step on the road of becoming a Sushi connoisseur.