Their unconditional loyalty, carefree nature and ability to cheer you up with the wag of a tail are all attributes that have helped the pooch become man’s best friend.

Yet for many owners, cuddly canines aren’t merely part of the family.

Blind, deaf and disabled people have long benefited from having the help of a hound, but dogs are fast becoming the difference between life and death in the medical profession.

Take the case of Rebecca Farrar for example. The six-year-old diabetic from Northamptonshire appeared on the BBC yesterday with her Labrador- golden retriever, Shirley, who saves the little girl’s life on a weekly basis.

That’s because the pooch, one of Britain’s only hypo-alert dogs, detects a change in odour when Rebecca is low on sugar – giving her a lick to let her know. This gives the youngster plenty of time to address the deficiency with something sweet so she doesn’t collapse and go into a coma.

Shirley was trained to detect the deficiency by the Cancer and Bio-detection Dogs charity, which helped pioneered this medical training with Coco, a chocolate Labrador from Broadstone. This pooch lives with owner Karen Ruddlesden, who suffers from a rare condition called Addison’s disease.

Although Karen and Rebecca’s conditions are very different, as far as detecting them is concerned “the principles are the same,” says Anna Webb, of Cancer and Bio-detection Dogs.

“Their dogs have been trained to tell them when they are having trouble with their particular condition,” she explains.

“Karen is alerted by Coco when her cortisol levels drop to a dangerous level and Rebecca is alerted when her sugar goes dangerously low.”

Their ability to detect such deficiencies is down to their receptive noses.

“A dog’s sense of smell is about a million times more sensitive than ours,” says Anna.

“Coco has been trained to smell cortisol and Shirley has been trained to smell hypoglycaemia, which they do through their owners’ sweat, skin and breath.”

The dogs will give early warning signs to their owners by licking them, prompting Rebecca to eat something sugary and Karen to take her medication. Without this advanced warning, both could become seriously ill or even die.

“He’s my knight in shining armour – with a tail,” says Karen, whose symptoms can include serious vomiting, lethargy and falling into a coma. “He’s totally changed my world. I became a hermit and lost all confidence because it was very embarrassing if I got sick when I was out. People would say ‘oh look at that drunk over there’. But since having Coco I haven’t had an Addison’s crisis.”

Karen now has her life back and has even been able to go abroad. “We were in Croatia earlier this year,” she says. “He’s totally changed my life.”