You can currently book an appointment (subject to availability) at one of the Dogs Trust's rehoming centres to get a free microchip for your dog.
The chip, which is inserted under the skin, includes a unique ID number which means if your dog goes missing, it is easier to trace, as the code can be read by radiowave scanners. Your details will also be stored on the microchip database. The process takes around 10 minutes and vets usually charge around £30 for the procedure. Any breed of dog, two months old or over, can be microchipped and there are no restrictions on how many dogs can be microchipped per owner, as long as you book an appointment in advance.
It is worth remembering the Dogs Trust is a charity, so if you are going to use its service, do consider making a donation.