Some police forces are using automated facial recognition technology to pick suspects out of a crowd. But is face mapping a valuable tool in the fight against serious crime or a new threat to our civil liberties? And does it work? Joshua Rozenberg investigates.

Also in this week's programme...

Do body-worn video cameras help police to deal more effectively with domestic violence incidents - or do they make matters worse?

And the mysterious case of the "pernicious weed"...who should pay when the wrong kind of vegetation - such as Japanese knotweed - is found on railway lines?

Producer: Neil Koenig