At present, all foreign teachers are required to convert their qualifications to QTS within four years of arriving.

BBC: Change may prompt teacher crisis

Total numbers of teachers in England's schools without QTS peaked in 2005, when there were 18, 570 and numbers have fallen since then.

BBC: Increase in unqualified teachers

In other state-funded schools, people employed as teachers have to have passed the relevant qualification - known as Qualified Teacher Status (QTS).

BBC: Warning of rise of 'unqualified teachers' in classrooms

Any teacher who has equivalent overseas qualification can join a school as an unqualified teacher and will be assessed for a year before he or she is deemed fit to take the QTS tests.

BBC: Change may prompt teacher crisis

Schools are also allowed to employ people called "instructors" who have particular - usually vocational - skills but do not have QTS, and the rules governing when they can be hired were relaxed last September.

BBC: Warning of rise of 'unqualified teachers' in classrooms