London, rather than Cambridge -- but have you dined at Rules? It's in Maiden Lane, tucked between the Strand and Covent Garden. It is where Bertie wooed Lilly Langtry and was favored by Graham Greene and other literary luminaries. It's the oldest restaurant in London. (Food-serving pubs predate restaurants, so you can find some much older pubs, but this is the oldest actual restaurant.) My favorite meal is Stilton soup followed by the wild Highland red deer. I'm sure everything is lovely, but I can't bring myself to order anything else at Rules -- it's one of the things I count on each time I visit London. They also have the best coffee I've found in Britain thus far.
As for pub grub, I've always cherished the Ploughman's lunch, anywhere it's served. It's just a large chunk of the local cheese, fresh bread, Branston pickle (like large chutney), a pickled onion, and a small salad. That and a pint of good cider, and I'm a happy camper.
And if you want a historic meal, there's a great pie shop on the main drag in Greenwich -- Goddard's Pie Shop -- that still does jellied eel and stewed eel. The first time I ordered it there, a French woman in line behind me pointed to it and told her children, "C'est un monument, comme le Palais Buckingham." Then, turning to me, she repeated in English, "That is a monument." I don't know the address, but you can't miss it. You come through the passage that connects the main street with the light railway, turn right, and it's within a block of the passage.