Just to balance things a little..the majority of people you will meet throughout Europe will be polite, helpful and trustworthy. Use common-sense in the typical pickpocket/scam scenarios (crowded metros, ATMs), as anywhere else and you should be totally fine. London taxis (Black Cabs) are totally kosher..avoid minicab operators they are unlicensed and uninsured. Don't purchase any tourist-passes touted on the streets of central London or the West-End area, promising free or discounted entrance to museums/shows etc - they are a contrick.