Fern was stolen from her three-year-old owner because she looks like Kate Middleton's dog Lupo (Facebook)

A lookalike of Kate Middleton's cocker spaniel Lupo has been stolen from its Surrey home.

Fern, a one-year-old puppy, was taken from the Ferrier family farm while playing outside with their other dogs, mongrel Megan, springer spaniel Cilla and collie Trio.

Jodie Ferrier, 31, said she believes a dog breeder spotted Fern and stole her to produce Lupo-looking puppies.

Since the Duke and Duchess of Cambridge got their pet dog in Christmas 2011, the number of cocker spaniel thefts has rocketed, with demand for the breed outweighing supply.

The Duke and Duchess of Cambridge got Lupo at Christmas, 2011 (Reuters)

The price of cocker spaniels has also gone up, with each puppy selling for up to £1,000. The average litter size is around five, and the gestation period is about two months, so puppy farmers can make around £5,000 on a fairly regular basis from each dog.

Ethan, the couple's three-year-old son, had fallen in love with the dog and is distraught that she has gone. "Fern is Ethan's puppy and he has been completely devastated since she was stolen," Ferrier told the Daily Express.

"He asks me every morning if Fern is coming back home today and I have to tell him I don't know - it's heartbreaking.

"Fern looks almost identical to Lupo and we've spoken the endless dog charities and police who tell us the same story - that demand for cocker spaniels is outstripping supply because of the popularity of Lupo.

Puppy farmers can make thousands of pounds from breeding cocker spaniels (Facebook)

"We want to make people aware of this problem, because it is getting worse ... We just want Fern back at home, and hopefully someone will come forward and she'll be back with us soon." ."

Surrey Police confirmed it was investigating the theft, while John Hockley, a rural communities officer, said dog theft was an "extremely emotive crime that impacts whole families".

Lupo has been blamed for the rise in cocker spaniel thefts in the past. In February, Lyn Randall, field trial secretary at the Cocker Spaniel Club, said: "The fact that Wills and Kate have a cocker did make a difference. Last year there was a surge in numbers, possibly for the wrong reasons.

"A lot more are being stolen now too and partly that is due to their rise in popularity, they do seem to be stolen to order."