See below for general points about pubs. Pubs are typically places where you can sample British cuisine. There are no such things as a British restaurant per se, so these will be your next best bet; even if you are against drinking alcohol, you will find a more traditional and full menu then a cafe or chippy.
Almost all pubs (see below) serve food, although not all will do so during the whole of their opening hours. Prices of all these types vary enormously, and you should seek local advice if you have particular requirements or standards. Do not sit at a table in a pub expecting a waiter to take your order for food or drinks: pubs nearly always work on a "queue at the bar for drinks: order at the bar for food" basis. You go to the bar to request and pay for drinks and food. To avoid annoying customers behind them, groups usually order as one, and "settle up" between themselves later (see elsewhere for "buying rounds"). You normally order your "starters" and "mains" together (food-oriented places have numbers screwed to the tables for you to quote, or will give you a number to take to your table). There is an etiquette that if you see another patron at the bar, you should invite them to order first. You then wait for your drinks to be poured and carry them to the table. When your meal is ready, it is either brought to you or, less commonly now, announced when it is ready for you to collect. The person who tidies away your main course may ask you what dessert you would like, or you may have to order at the bar again.