Whoops, accidentally posted before I had finished!
So yeah, three year undergrad, followed by three years doctoral training where you combine teaching, research and clinical placements (at least one placement will be working with children and/or adolescents). However, getting onto a clinical training course is renowned for being highly competitive, so you will need to boost your chances by getting a couple of years of relevant work experience and considering post graduate study to bolster your application. It is exceedingly rare to go straight from your undergraduate degree onto the doctorate.