Another tip, especially for those who will be visiting London for the first time and who are not used to urban travel by public transport in a major city (i.e this would exclude New Yorkers or Chicagoans) - you will be traveling by tube (subway) on a daily basis while in London. Some of these journeys may well be at peak hours in very crowded carriages. That is where the (obvious) tourist is most vulnerable to 'attack' by professional pick-pockets.
I think that hanging your passport around your neck is possibly a little over the top for London, but certainly keep it in a safe inner pocket. Ladies, keep your handbags closed and under tight control when in a crowd. The rest is just common sense.
edit - the contents of Cathy's case are likely to be pretty amusing, when she gets around to posting them! Of course, as a (now) experienced trans-Atlantic traveler, she'll be packing at the last moment.
RIP Iron Man
Rock On and keep the Faith