"The police force should not be enticing people to commit crime... And that is what they have been doing," says James Daniels, a small-time villain who claims he was set up by a police informer on a major firearms charge, although the charge was later thrown out by a judge.

Informants, grasses, narks - whatever they are called, they have always played a vital role in the police's fight against crime. However, disturbing evidence is revealed in tonight's programme that informants are now being used to set up crimes so that the police's success rate is boosted.

John Penycate examines the work of three police informers and uncovers a pattern of set-ups, pay-outs and headline-making arrests that points to a corruption and devaluation of the system.