A fake pet passport and microchip was all it took to convince border control on both sides of the channel that a toy dog was a real pet.

Staff repeatedly failed to look inside the crate, which would have immediately identified 'Mitzi' as a stuffed toy.

The charity behind the stunt says the failings highlight just how easy it is to smuggle animals into the UK using Defra's Pet Travel Scheme.

The lax enforcement allows unscrupulous breeders to bypass the required health checks.

The Dog's Trust says breeders from Lithuania and Romania are supplying puppies under twelve weeks of age – the age they can be vaccinated against rabies.

The charity also says Lithuanian and Romanian vets are falsifying data on pet passports, removing and replacing laminated strips and filling in fictitious details.

As proof, the charity bought eight passports from seven vets in Lithuania who falsified data on the documents in order to allow puppies under the age of 15 weeks to travel to Britain.

Watch: The Dogs Trust successfully smuggles a stuffed toy dog across the channel

Laura Vallance, head of public affairs at the Dog's Trust, said: "We found vets who were willing to falsify passports. They were willing to fake rabies certificates, and they were willing to lie about the puppies' age.

"A lot of these dogs are coming from countries that do still have rabies, but they could be carrying other diseases too."

The fake passport used by the charity did not match the microchip, taped to the inside of the crate.

And the rabies vaccination connected to the passport was out of date.

"This 'dog' should never have got into the UK," Ms Vallance said.

"We want to see Defra get a bit more of a grip at the border. We'd like to see visual inspections so the people enforcing the legislation know the puppy in the crate matches the passport.

"And we'd like to see fixed penalty notices at the border so there is a real deterrent for those trying to break the rules."

"We'd also like to see more intelligence-led investigations to make it more difficult for the people who are actually bringing these puppies in."

Puppies smuggled into the UK illegally are often small, fashionable breeds such as french bullldogs and pugs, which can sell for up to £2,000 per animal.

The first time many owners discover their pet has been smuggled in is when they take the puppy to the vet.

If the dog has not had the proper vaccinations, it means they have to go into quarantine for six months.

Defra has defended its procedures and argues the responsibility for preventing puppy smuggling rests on the authorities in their country of origin.

A Defra spokemsn said: “The UK has one of the toughest pet border checking regimes in the EU and the most reliable way to prevent illegal puppy smuggling is to scan the microchip and ensure that the dog has a matching passport.

"Every single dog travelling to Britain is checked in this way. Microchips can be scanned through carrier boxes which is why the dogs were not seen in this case.

“Responsibility for stopping the illegal movement of puppies begins in the country where they are born so we do have some concerns about the ability to gain fraudulent passports in some countries.

"The Chief Veterinary Officer has already written to authorities in Lithuania and we will be investigating how fraudulent documents were obtained in this case."