A growing proportion of secondary school teachers have left the profession, according to a Department for Education analysis.

The news has led teachers leaders to warn that schools are becoming “unpleasant places to work”.

The research on teacher supply published today shows that between 2011 and 2015 the overall “wastage rate” increased in every subject at secondary level.

Wastage refers to those who have dropped out of the profession, teachers who have retired and those who have died in service. The rate is calculated by dividing the teachers who have left the profession in a given year by the total number of teachers.

According to the DfE’s figures the overall wastage rate change for secondary schools increased by one percentage point, from 10.2 per cent in 2011 to 11.2 per cent in 2015.

The DfE said this was driven by an increase in those moving to go “out of service” - qualified teachers who are not identified as teaching in either a state primary or secondary school in the government’s annual workforce statistics, but who were teaching the previous year and are also not claiming a pension.

The proportion of teachers going out of service rose from 6.6 per cent in 2011 to 8.7 per cent in 2015.

Sciences and Technology subjects have the highest wastage rates, and the Humanities and PE have the lowest wastage rates.

Mary Bousted, general secretary of the ATL teaching union, said she was “not surprised that the level of drop outs are increasing”.

“Unfortunately, the way things are going it’s going to get worse,” she added.

Dr Bousted said teachers were leaving the profession because of a “toxic mix” of  pay restraint and excessive workloads.

“In many places now schools are becoming really quite unpleasant places to work because staff wellbeing isn’t being taken into account,” she said.

“What we do with our teachers is we burn them out and we don’t treat them with professional respect.”

The DfE analysis also looked at what factors most affect teacher retention.

The odds of leaving the profession are highest at the beginning of a teachers’ career, and staff on fixed term and temporary contracts are more likely to leave teaching.

Teachers with five or more days of sickness in the year previous to their departure are more likely to leave.

The analysis also found that the likelihood of teachers leaving the state sector is highest in schools rated ‘inadequate’ by Ofsted.

“Regardless of whether we look at teachers or leaders, primary or secondary schools, the odds of leaving are more than twice as high in ‘inadequate’ schools than in ‘outstanding’ schools,” the paper states.

London has the worst regional retention followed by the South East, and the North East has the strongest retention.

However, the DfE said deprivation did not appear to directly influence retention.

“The deprivation of schools’ area does not seem to be a major driver of in-system teacher retention once the other characteristics are controlled for,” the paper said.

But it added: “[Deprivation] is likely to feed in through the relationship between deprivation and other predictive factors”.