I have always understood it to be the case that to teach in state schools you need to have Qualified Teacher Status.
http://www.education.gov.uk/get-into-teaching/faqs/becoming-a-teacher/qualified-teacher-status
Private schools, and now free schools do not have this restriction. As of last year, the coalition relaxed the QTS requirement for Academies too, so that they to in theory can hire teachers that do not meet the QTS requirement.
Is it a good thing or a bad thing? Probably mixed. As ymb has pointed out, there are plenty of people who have come through the private schools system without necessarily having been taught by a "Qualified Teacher" and done well. Does this mean QTS is unnecessary? Cannot tell from that, because there are additional confounding factors, like class size, parent motivation, money, all of that.
The fear - and possible downside- of not hiring QTS teachers is that some free schools will hire any old yahoo on the cheap, or someone who fits their religiously inspired criteria. The upside might be that you get access to a wider range of potentially more inspirational and hence effective teachers.
Experience in the real world is a fine thing - but it does not, of itself, guarantee a better standard of teaching.