The Dover Street Wine Bar, on Dover Street offers a menu with more than just fish & chips, of course. And in the evenings you often have live music. In fact it can be a bit of a meat market. This sizeable restaurant and bar is actually in the basement, with just a doorway leading in from the street, so it's easy to miss.
The best time to go for fish & chips is at lunchtime, when they have a special lunch menu that offers a variety of options plus a drink of your choice priced at between 6 and 10 pounds. The fish & chips is on the 10 pound list, which I always find a little surprising. Still, it's quite good, albeit a little small. The chips are nice, and the atmosphere is that of a fairly upmarket restaurant.
Favorite Dish: I usually have the fish & chips, although other lunchtime favourites include things like bangers and mash, risotto, chicken and chips, etc.