Veg Out is a wonderful option (in a place with very little vegan options) in London.
The fish and chips are wonderful, along with their desserts. It is by no means healthy though, as most stuff is deep fried and full of fat. It's a great Vegan Junky Food menu though.
The staff tend to be hired based on how feminist/vegan they are, which isn't a bad thing, except that some of them aren't the best wait-staff.
The location is wonderful, right downtown in an adorable renovated old London home.
Cons: staff, crowded at times (slow service), not the cheapest