To be able to teach in a state-maintained school you need to have Qualified Teacher Status, and it can take quite a long time to become a fully qualified teacher.
There are different stages an individual must go through before they can achieve QTS and you can take an initial period of teacher training (ITT). There are a formal set of skills and qualities required to be a teacher and the QTS is essentially a bare minimum for quality control.
Another route in to get your QTS is to complete your training at undergraduate or post graduate level, while you can even take an employment based route, where you employers provide the training for you. If you’re looking to become a teacher make sure you know about the qualified teacher status, because you’re certainly going to need it any public school.