Pet owners have been warned to be vigilant by the Kennel Club when buying White Swiss Shepherd dogs amid fears premium priced puppies are being passed off as their cheaper German cousins.

The breed has fast become one of the most sought after in Britain since it was brought over in 2008, with its stock set to rise further next week when the dogs compete at Crufts for the first time.

There are fewer than 100 White Swiss Shepherds across Britain, but rapid demand has risen to the point that breeders have told potential owners they face a four-year wait for puppies.

Canine experts now fear increasing appetites for the dogs has caught the attention of rogue dealers.

The Kennel Club has intervened on the eve of the world's most famous dog show following intelligence from enthusiasts about one dealer in South Wales who attempted to sell a white-haired German Shepherd as a White Swiss Shepherd.

Sue Renno, breed club chairman at the White Swiss Shepherd UK Club, told the Telegraph said: "There is no doubt that some people are looking at this trade as a cash cow.

"A White Swiss Shepherd puppy cost £1,500 while a German Shepherd puppy is about £900. They look very similar and we know of one case already. I'm not going to name the dealer but know who it is and are keeping a careful watch on them.