On London's streets neighbours cower behind barred and bolted doors - watched over by CCTV cameras - while former soldiers pound the pavements with guard dogs, ready to respond within minutes of a panic button being pushed.

This is not an inner-city sink estate, however, nor a futuristic vision of a lawless city, but wealthy enclaves such as Kensington and Chelsea, Belgravia and St John's Wood, where the well-heeled are willing to part with £1,000 a year for private security patrols, such is their fear of crime.