As from April 2016 it became a legal requirement that all dogs over 8 weeks of age must be microchipped and the details registered to an authorised commercial database.
If buying a puppy from a registered breeder or rescue centre this will almost certainly have been done. You must make sure that all the details logged on the database are up to date.
Your dog’s microchip must be fitted by a trained professional; for example a vet, and there is a small charge, usually around £20 for doing so. Blue Cross centres, Battersea Cats & Dogs Home and The Dogs Trust will microchip your dog for free.
It is a quick and relatively pain free procedure. The microchip is about the size of a grain of rice and is injected under the skin between the shoulder blades. There might be a sharp pain when the cartridge containing the microchip goes through the skin as the needle is quite big compared to the normal injection needles, but it is very quick and most dogs don`t react.
The cartridge is held in place for a few seconds and withdrawn slowly to ensure the microchip remains in place. Very occasionally there can be a small amount of bleeding but there is no pain after the initial injection. The chip sits in the small dip between the shoulder blades so it is not usually palpable. It doesn't usually move but sometimes it can travel over one side but rarely migrates further than the shoulder blade.
Microchips are read with special scanners that all veterinary surgery's and rescue centres have. The scanners read the individual barcode on the chip and this is translated into a corresponding number unique to your dog which is logged in the national database against your details. If your dog is picked up the chip can be read immediately if taken to a rescue centre or vets and you can be contacted straight away; highlighting the importance of keeping all your details up to date.
Rarely microchips will stop working. If this happens it is quite ok to re-chip your dog with no detrimental effect.
Under the Control of Dogs Order, it is also a legal requirement for dogs in a public place to wear a collar with a tag containing the name and address (including postcode) of the owner. Telephone numbers are optional but recommended. There can be a fine of up to £5000 for failure to do so.
If you have any concerns about your legal obligations please speak to your vet.