London's Inside Out team investigates the trade to find out how these farms treat man's best friend.

Elizabeth Reeves visited a pet shop in London to buy some food for her dogs, but when she saw the puppies in there she immediately took pity on them.

She bought one, Crystal, and took her to the vet who said the dog was under weight, had a bad form of intestinal worms, kennel cough, bad eyes and was anaemic.

Crystal was severly underweight

RSPCA Inspector Ian Gough said: "The shop that sold Crystal got its supplies from Ireland.

"It's an ever-repeating story. Thankfully she survived but not all of them survive, some of their illnesses are so bad that unfortunately they die."

He explained that puppies are being mass produced at the farms so the bitches are "continually breeding which means that the quality of the animal is not good".

"The welfare of the animal is not considered and they are being kept in squalid, dirty, horrendous conditions."

'Personality problems

The pups are often left alone in cramped isolated environments with little supervision and very little love.

Puppy farms have now moved off-shore to places like Ireland as England has strict new regulations enforced by the government through local councils.

Vivienne Phillips, a registered breeder, told Inside Out that dogs bred in puppy farms are "quite often lacking in bone because they have been taken away from their mother too young".

"And secondly they haven't been socialised so very often they have got personality problems."

Inside Out is on BBC1 at 1930 GMT on Monday.