Vets will be legally required to check dogs' microchips before putting them down, to stop healthy pets being killed "completely unnecessarily", under a change being championed by Boris Johnson.
A planned Animal Welfare Bill is expected to include "Tuk's law" - a statutory requirement for vets to check that those seeking to euthanise dogs are the animals' registered keepers.
The move is understood to have been ordered by the Prime Minister who, together with his fiancée Carrie Symonds, adopted Dilyn, a rescue dog, shortly after entering Downing Street last year. A No 10 source warned of an "alarming" increase in reports of healthy dogs being put down.
It follows a campaign in the name of Tuk, a rescue dog put down at the age of 16 months after being rehomed.
Campaigners say that, had the vet who euthanised Tuk scanned his microchip, it would have become apparent that the person asking for him to be put down was not his registered keeper. The chip also contained details of the dog's original rescuers, who could have taken him back.
James Daly, the MP for Bury North, who has championed the proposed law in Parliament, said it could prevent neighbours annoyed by barking dogs from taking them to vets to be put down. The campaigners behind Tuk's law say they have received support from Lord Goldsmith, who is now the minister for animal welfare, as well as Ms Symonds, a conservationist and animal rights campaigner.
A No 10 source said: “The rising reports of perfectly healthy dogs, particularly from rescue, being put down is alarming. We are a nation of dog lovers and this goes against every grain of that.
“When something so simple as checking a microchip can prevent this it is clear we need to take action. Since we introduced compulsory microchipping for dogs in 2016 we have seen a clear drop in the number of stray dogs on our streets and an increase in the number of lost or stolen pets reunited with their owners.
"Now we need to put this technology to use again to stop pets being killed completely unnecessarily."
The measure is expected to form a part of the Government's Animal Welfare Bill, which will be formally unveiled in the Queen's Speech next year. The legislation will also include tougher sentences for animal cruelty and legislate against trophy hunting.