Keith Waterhouse is very particular about what lunch is not: 'It is not prawn cocktail, steak and Black Forest gateau with your bank manger. It is not civic, commemorative, annual office or funeral. It is not when either party is on a diet, on the wagon or in a hurry.' He is equally precise about what lunch is: 'It is a mid-day meal taken at leisure by, ideally, two people. Three's a crowd, four always split like a double amoeba into two pairs, six is a meeting, eight is a conference... A little light business may be touched upon but the occasion is firmly social. Whether they know it or not,...