Visited London recently and went to Yo Sushi.  Chain fast food sushi that is served to you on a belt that moves around the restaurant.  You pick up the sushi you want and they charge you based on the color of the plate. 

With the high exchange rate and our effort to eat healthy still, this was a nice find.  Reasonable price and the sushi was nice.  Service was quick and you can fill up your water (gas or no gas) with a pump right there at your seat.