Dogs can recognise drugs including heroin, cocaine and rohypnol

Surrey Police said the animals were the latest weapon in the force's crackdown on drugs supply and use.

The canines are currently being trained to detect chemicals like rohypnol and GHB, used as date rape drugs and notoriously difficult to detect by taste, smell or sight if added to drinks.

"As new drugs become a problem, the dogs are taught to recognise them," a Surrey Police spokesman said.

While they may appear soft and friendly, they should strike terror in those involved in the supply of illegal drugs Superintendant Kevin Deanus, Surrey Police

Police dogs operate in two ways and can recognise substances including cocaine, crack cocaine, heroin, ecstasy and cannabis.

Passive drugs detection dogs pick up the scent of an illegal substance in the air and follow it to its source, at which point they indicate the suspect to the handler.

Pro-active animals are taught to search areas for drugs, both in the open air and within buildings.

They are being used in town centres to disrupt drug dealing in pubs and clubs, the spokesman said.

Superintendant Kevin Deanus, who is leading Surrey Police's anti-drugs campaign, said: "Dogs are becoming a vital part of our war on drugs.

"We use a variety of breeds and their training is becoming more and more effective.

"While they may appear soft and friendly, they should strike terror in those involved in the supply of illegal drugs in Surrey."