The Dutch police are pioneering a new approach to catching criminals, recruiting rats to sniff out crime.

The new recruits, learning that crime really does stink, are called Derrick, Thomson and Thompson, Magnum and Poirot, so they have a rich literary legacy to live up to.

‘Employed’ by the Dutch police innovation centre, their ‘boss’, the police officer in charge of the project, Monique Hamerslag, said she got the idea from the way rats are used in Tanzania to sniff out landmines.

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Rats can learn to sniff out any odour, from drugs to explosives. In the future they could even sniff out blood or money to help to move along investigations.

Costing much less than dogs both to keep and to train, rats need only 10 to 15 days to learn to distinguish a certain smell. Tea strainers containing different substances are attached to the cages and when the rat detectives identifies gunpowder, they are rewarded with a ‘click’ sound and a sunflower seed.

Although their olfactory evidence can’t be used in court, Ms Hamerslag said she hoped it would be useful to focus investigations, showing forensics where to search for information about their suspects.

Perhaps surprisingly, given rats’ fearsome reputation, the main disadvantage to using them in investigations is their shyness.

"It's best to bring the smell to the rats and not the other way round," Ms Hamerslag told AFP. "That means we have to take samples and bring them to where the rats live.”

Dogs will therefore stay on at the force as their predatory natures means they are much happier exploring unfamiliar places