Nearly 300 teachers are working in Croydon's classrooms despite not being qualified, figures have revealed, leading a senior MP to claim the borough is "a test lab" for education policy.

Croydon's schools employ 293 teachers without formal qualified status, a rise of 57 per cent since the Government loosened restrictions on academies in 2012.

The "staggering" rise, which far outstrips a 16 per cent national increase and 26 per cent jump across London, was cited by shadow education secretary Tristram Hunt in an attack on Department for Education (DfE) policy.

He told the Croydon Guardian: "It is almost as if the borough is used as a test lab for the very worst Government policies.

"The key to school improvement lies in better quality heads and teachers. This means making sure the best teachers teach in areas like Croydon.

"It does not mean flooding schools with unqualified amateurs who stand no chance of controlling unruly year nines."

In summer 2012 the Government removed restrictions to allow academies, as well as free schools, to employ unqualified teachers in a move ministers claimed would allow talented experts to work in classrooms.

Since then, 26 schools in Croydon have converted to academies. Thirty-nine of Croydon 108 state-funded primary and secondary schools are now either academies or free schools, with another five set to become academies in September next year.

According to the DfE's statistics, the borough's unqualified teacher headcount has risen from 187 since 2012, although the true tally likely to be higher as the figures only cover up to November 2013.

Graham Cluer, spokesman for Croydon branch of the teaching union NASUWT, said the figures were "a cause for concern".

He said: "There are occasions when it would be perfectly legitimate to employ a teacher with no formal qualifications, but those are really short-term on-the-job training schemes where they are working towards qualifications.

"To employ teachers on a permanent contract when they are not training - the sort of thing that academies are allowed to do - is extremely worrying. I think it is appalling, in the same way I would worry if I went to hospital and was treated by an unqualified doctor.

"It is not improving education, it is opening the door to a much worse quality of education."

Mr Cluer added some of Croydon's academy providers - Pegasus, Reach2 and the yet-to-launch STEM - have assured the union they will not employ unqualified teachers.

A DfE spokesman said: "We believe that it is head teachers who are best placed to decide who to employ in their school.

"It is only right that they should have the choice of complementing their teaching staff by bringing in experts from the world of science, literature and art to enrich pupils' learning.

“Nationally, the number of teachers who don’t hold qualified teacher status has fallen since 2010 and the overall quality of our teaching workforce continues to rise, with a record 74 per cent of new teachers holding 2:1 degrees or above."