Also, don't forget to look the "wrong way" when crossing the street. You'd be surprised how much looking to your right before stepping off a curb in ingrained into your habits. And you can easily be killed -- literally -- by that habit in the UK. Look both ways, especially left.
And I think that many here are being much too harsh with British food. There are now some very good British restaurants. As mentioned, the River Cafe is very good.
http://www.stjohnrestaurant.com/menus/ for lovers of offal and exotic cuts of meat.
http://www.thefatduck.co.uk/ Not in London per se. About 25 miles west. But an amazingly good restaurant. Arguably one of the best in the world.
http://www.hibiscusrestaurant.co.uk/ Not British, but my favorite French restaurant in London. Medium sized, but very well selected wine list.
http://www.boisdale.co.uk/belgravia/ Scottish ingredient driven seasonal cuisine.
http://www.marketrestaurant.co.uk/ more modern spin on traditional British food.