For a casual but great food experience (ie English Food), I recommend St. John's Bread and Wine. Although the food is simple, it is always very seasonal and comforting. For the fine dining experience, I will go for Marcus Wareing at the Berkeley Hotel. I heard there's a chef in the kitchen reinventing the menu along side Marcus Wareing. The chef is heard to be from a strong resume including Thomas Keller's per se in New York and Rene Redzepi's Noma in Copenhagen.