The latest weapon in the fight against crime took to the streets for his first day on duty yesterday - Britain’s only Staffordshire bull terrier police dog.

Former rescue dog Kos, a black and white Staffie, was saved from an uncertain fate in a rescue centre.

He was trained by Avon and Somerset Police dog handler PC Lee Webb after being donated to the force by an RSPCA rescue centre 18 months ago.

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Policeman's best friend: PC Lee Webb with Kos, the first Staffordshire bull terrier cross police dog

Hounding criminals: Kos comes from a rescue centre and could have been put down but for PC Webb's intervention

Focus: Police dogs need an enormous amount of discipline to do their jobs effectively

The breed has a bad reputation and is associated with 'hoody' owners because of its muscular appearance and tough nature.

But Kos has become the first of his breed to be trained to detect drugs, currency and firearms.

He went on duty first thing this morning and got off to a flying start when he found a lump of heroin in a car which was pulled over in Bristol.

PC Webb said: 'Like many breeds, Staffies can be tarnished with a bad reputation, which is unfair.

'But Kos is the gentlest and kindest of dogs. He’s always been very playful and he absolutely loves the game of searching.'

Rambunctious: Kos, (front) and three other police dogs enjoy a morning off police work

Police usually train Springer Spaniels or Weimaraners as their temperament is more suited to learning the extreme levels of control necessary to become a sniffer dog.

PC Webb said: 'It didn’t take any longer to train Kos than the Spaniels we have, and some of those are also rescue dogs.

'We start them on toys and then train them on the scents, which they come to associate with play.

'Kos was very excitable on his first day on the job - he absolutely loves it.'

The two-and-a-half year old dog was being cared for by Sue Dicks at the RSPCA's West Hatch Animal Rescue Centre near Taunton, Somerset.

PC Webb said: 'Sue Dicks is amazing. She’s always got an eye out for dogs that would be suitable for us to train.

'She looks for any potential, which we could train to become valuable assets to the force.'

Kos, like all other drugs dogs has an above average ability to search and great determination to play fetch and search for things.

Experienced trainers like PC Webb, who has been training dogs for ten years, nurture these traits in order to turn them into working dogs.

The dogs usually take six weeks to train, and have a career of eight to ten years.

But lively Kos took several months to train, because PC Webb did it in his spare time.

PC Webb said: 'I would train him whenever I had a spare 20 minutes or so. He was a quick learner, but it still took longer than usual.

'I’m a dog person - it’s not just a job for me, they are part of our family.'

Search: Police dogs are trained to detect detect drugs, currency and firearms

Early victory: Kos found a stash of heroin on his very first day

Kos was donated to the animal rescue centre after he was involved in a number of fights with a sibling.

PC Webb said: 'He’s a lovely dog, but he has quite a few scars from fighting with another dog when he was a pup.

'If he hadn’t been successfully rehomed, he may have been put down, as Staffies are a breed with a bad reputation.'

He now lives at home with PC Webb and his three other dogs - two of which are Spaniels training to become drugs dogs.