On the evidence

Det Supt Mark Jackson discovered last year, in a Cambridge University research course designed for police leaders, that 42 per cent of the homicides in London over a decade were concentrated in just six per cent of the tiny places known as 'micro-areas'.

Instead of a murder map of London featuring three or four bright red high-homicide boroughs out of the 32 in the capital, he found the map showed red homicide spots spread all over the Met's territory. Det Supt Jackson's research findings showed the importance to police efficiency, and to budgets, of basing investigations on rigorously tested evidence.

The two key components of evidence-based policing, as used by American police heads such as Bill Bratton (formerly New York City Police commissioner and chief of the Los Angeles Police Department) are prediction and prevention. Discoveries such as Det Supt Jackson's homicide analysis are vital to Mr Bratton's strategy of 'putting cops on dots' where crime is high.