All dogs must be microchipped by a vet and registered on an authorised database by the time they are 12 weeks. This also applies if a dog leaves the property where they were born before they are 12 weeks. The regulations are set out in the Microchipping of Dogs Regulations 2015.
From 1 February 2020, if you are advertising a dog for sale, the advertisement must have the dog’s microchip code.