As many as one in three dog owners could be buying their pet from puppy farmers, the Kennel Club has warned.
Research by the organisation found that of more than 1,000 owners of pedigree, pure-bred, cross-breed and mixed-breed dogs, 14% bought their puppy from a pet shop, 7% used the internet and 16% responded to a local paper advert.
The Kennel Club is warning that all three outlets can be used by puppy farmers, who breed too many litters from female dogs that are kept in bad conditions and whose offspring are likely to suffer ill health and behavioural problems.
It is launching a new "stop puppy farming" campaign urging people to spot the signs of an irresponsible breeder, report suspected puppy farmers and opt for the Kennel Club's assured breeders scheme or a rescue dog.
According to the club, puppy farmers commonly sell puppies over the internet or through pet shops so buyers cannot see the "cruel" conditions the dogs are reared in.
It wants to see tougher rules to clamp down on puppy farming, with all breeders forced to follow the standards it sets for its Kennel Club Assured Breeders Scheme, which include a safe, clean environment, health tests for parent dogs and providing a contract of sale.
And it is calling on prospective buyers to make sure they see the puppy in its breeding environment with its mother and not to buy a dog if they have any concerns, even if they want to "rescue" it, as it gives the breeders money.
Buyers should check what health tests and certificates there should be from the parent dogs, even if they are buying a cross-breed, and ideally the puppy should be micro-chipped.
Marc Abraham, Kennel Club veterinary adviser, said: "There is now an alarming trend which is seeing breeders view dogs just as commodities without any regard for their rights as living creatures. People wouldn't buy a car from a dodgy dealer, offering no MOT or service documents, but sadly people don't ask for the similar assurances from a dog breeder."
The Kennel Club is launching a film as part of its campaign to stop puppy farming, which can be viewed at www.thekennelclub.org.uk/stoppuppyfarming