I was walking around Borough Market this morning and saw a handwritten note taped to a lamppost, it said "Lost? Purple wallet, American cards, at Brindesa" Brindesa being a nearby restaurant.
We are generally an honest and helpful bunch in London and i've heard many stories of people losing things and getting them back, my wife on a couple of occasitions.
The point of my post is... Firstly look after your things, but at least put something traceable in your possessions, like a card from your Hotel, or a friends or your own mobile number. You might just get your stuff back and save a ruined trip to my wonderful city.