How to stop pick-pocketing on the London Underground

I have been researching crime on public transport systems around the world for over 15 years, and when Transport for London (TfL) contacted me to assist them in tackling pick-pocketing on the London Underground I realised they faced a new challenge. Recently the use of foot patrols targeting crime hot spots have proven to be an effective crime reduction measure, for example in Manchester, and, further afield in Philadelphia. However, there are a number of problems with introducing this approach to dynamic and transient systems such as the London Underground which have a continual movement of passengers and infrastructure, and therefore the hot-spots tend to move fairly rapidly.