Ikkyu, Japanese restaurant
67a Tottenham Court Road, London W1T 2HE
This is on the left hand side of Tottenham Court Road, just down from Goodge Street tube station. You have to keep an eye out for the little back doorway (or you'll miss it) that leads down some stairs to the restaurant itself.
I sat at the counter and had the nigiri sushi set which was very good. The rice part of it was excellent and worlds apart from the sushi stuff you get from M&S.
It got very busy for lunch and was full by 1pm, so get there early.
Lunch cost me about £12 which is a bit extravagent but I did have two teas and an ice cream. I would definitely go back.