There are a few restaurants in London under the Kulu Kulu banner but I think the best one is at South Kensington. It might not be but I like it the best. Kulu is affordable Sushi and you can normally get out happy for under £10. Awesome. Free green tea I think, never looked at the bill.
It is a Sushi Train style but so fresh, the Salmon will melt in your mouth and this is a place I have been to more than once. Don't go into Yo Sushi - find a Kulu Kulu.
Two maps attached for Sth Ken and Soho
Sth Kensington
39 Thurloe Place, London, SW7 2HB - ph 020 7589 2225
Soho - Kulu Kulu