Why is there a shortage of teachers?

The two largest teaching unions in the UK, the NUT and the NASUWT, are meeting for their annual conferences this weekend.

One thing they are likely to be discussing is concern over a growing shortage of teachers.

A recent report by the National Audit Office said the government had missed recruitment targets for teachers in England for four years, but the Department for Education says overall teacher numbers have risen.

The BBC's Education Editor Branwen Jeffreys explains.