Glitch, sorry - hate the new site!!
Where I work, the vast majority of teachers have a teaching qualification plus subject degree (or doctorate). You might get one or two older teachers who don't have a PGCE but have 30 years of teaching experience to make up for it, or very very occasionally a newer member of staff who hasn't done a teaching qualification (perhaps has been teaching overseas), but is an exceptionally good candidate so is chosen over and above a qualified teacher. But we'd never employ an unqualified teacher just because we don't care about teacher training, or because we can't find someone who is qualified.
Similarly, with teaching practices, we do lots of CPD and keeping up with new developments - we've got the time and the money to do it. In fact, we quite often support local state schools with this, because they don't. We're not dependent on the government telling us how we need to teach, so we're free to innovate when we want to.
Of course, there might be some private schools where the teaching isn't great, but to say that 'many' schools are employing poor teachers is just nonsense. If anything, I'd say the recent MN thread on teacher recruitment in the state sector is well worth a read... There are some great schools and great teachers in the state sector, but there's also a massive recruitment and retention crisis, with lots of teachers bewailing the current state of affairs, and parents complaining that their children have had a succession of primary classes taken by TAs or secondary classes under long term cover.