Brakspear Organic Beer, widely available. Clean tasting, hoppy aroma, well balanced with a moderate, toffee & bitter-honey finish. As English as squashing wasp's in August. Lovely.
Have you tried the Bath Ales Wild Hare which Asda sells? I don't frequent Asda but its worth a visit since this is a nice hoppy golden ale that is great on a warm evening.
Marston's BB is an excellent session beer and does the decent thing of coming in a 750ml bottle. However, Pedigree and Double Drop are better beers.
Outside the hallowed walls of Marston's there is always the ever-consistent Landlord and the delights of Bluebird, all available from Morrison's at £5 for four.