What are the best restaurants in Central London that aren't too expensive?

Looking for a nice restaurant which isn't too expensive in central london or just outside the city centre. Been looking on google but i think its hard to choose. Would prefer British or Italian restaurants please. Its for an anniversary meal so i'd like a place were i wouldn't feel over dressed in a dress and heels but not to fancy that my boyfriend would have to wear a full suit (smart jeans or black trousers and a skirt and shoes).