It is law (in the UK) that all dogs must wear a collar and tag. From 2016 a law is being introduced so that microchips are a requirement. Another long established method is a tattoo.
It is of course natural to want a system that not only allows a dog to be identified and returned to the owner (or the owner to be made known where other circumstances apply). It is also beneficial that if the dog is lost or stolen that is has a form of ID that cannot be removed. But this should be with the 'first do no harm' principle.
Tattoos have been used for decades and the system in place does work, although there is some question about whether 'first do no harm' really applies. And thieves have taken drastic measures to remove tattoos.
Microchips are a good idea in theory, but in practice this system is fraught with problems including that of health, and it is unlikely that it would be 'policeable'. More likely that it will make plenty of money for the manufacturers, vets and those charities and others who will benefit from sales, but in reality will be another 'dog licence' charade.
Whichever form of ID you choose it does rely on the finder knowing who to contact. This is a flaw in all the systems where visible ID is not available such as when a dog is stolen, no system will prove effective if the thief is not caught or the dog is not found.
As usual, the 'authorities' take a commercial and sensationalist approach (especially where the dangerous dogs act is concerned) that does not truly look at what works best, so end up with yet another flawed system that penalises the ordinary dog owner (and dog) with little reward in respect of what they were trying to do in the first place.