I've been trying to find out the extent of this for a while.
Basically people are taken on by schools as 'Teaching Instructors'. They cover lessons but have the work set for them and do not mark it. They must have a degree but do not need any other qualification.
Here is an article about it (with some interesting comments at the end)
I finally met someone who was working as a 'Teaching Instructor' recently. He had graduated the previous year and was doing it as short term employment whilst he 'worked out what he wanted to do with his life'.
He said that the work was always set for him and he hadn't been asked to mark anything. He told me that the SMT bloke hiring him explained that he was basically a 'Supply Teacher but Cheaper'
He started off covering the subject he had a degree in but after a week, the school offered him work doing general cover. He was paid £95 per day and had been working for three months. He told me that "It's been interesting but there's no way I'd go into teaching". He was incidently, very impressed by the 'real teachers' he had met. (Except for me, I suspect)
It does raise a few interesting points:
1) How widespread is this practice? I think there are probably thousands of them, but I cannot say for certain.
2) Presumably the parents have no idea what is going on.
3) How different is this situation from having Supply Teachers? I regularly covered subjects that I knew nothing about for weeks on end.
4) How on Earth did this get to happen without the Unions doing anything effective to stop it?
5) Would you be happy going to see your doctor and hearing "Dr. Jones is away today but I'm a 'Medical Instructor'. What seems to be the problem?"