Labour warns of 60% four-year rise in unqualified teachers
There are 24,000 teachers without formal teaching qualifications in state schools in England - an increase of more than 60% in four years.
It means that more than 5% of teachers do not have qualified teacher status.
Labour, which highlighted the figures in the annual school workforce survey, said the increase in unqualified staff was "threatening standards".
Head teachers' leader Malcolm Trobe said the use of unqualified staff reflected the wider teacher shortage.
A Department for Education spokesman said: "The number of teachers overall has risen by 15,500 since 2010 and the proportion of qualified teachers in schools remains high."
But the shadow schools minister Mike Kane said: "The government have completely failed in their most basic of tasks and are clearly relying on unqualified teachers to plug the gaps.
"There is nothing more important to a good education than excellent teaching. The Tories' failure on teacher recruitment is putting school standards at risk."
Labour claims that if these 24,000 unqualified teachers had classes of average size of 25.5 pupils, it would mean more than 600,000 pupils being taught by teachers without qualified teacher status.
The figures show the number of unqualified teachers in 2012 had been 14,800. This had risen to 24,000 in 2016.
In terms of full-time equivalent posts, it means that 5.3% of teachers in 2016 were unqualified, compared with 4.9% in the previous year.
But about a fifth of those unqualified staff were working towards getting qualified teacher status (QTS).
A higher proportion of unqualified staff are in academies and free schools. In local authority secondary schools, 4.9% of teachers are unqualified, but in secondary sponsored academies there are 9.6%, and 11.3% in secondary free schools.
Mr Trobe, leader of the ASCL head teachers' union, says this increase in unqualified teachers is linked to "recruitment difficulties" facing schools.
He says schools need to put someone in front of a class, and "there are not enough qualified teachers out there".
But he says that schools have always needed some staff with specialist skills - such as for vocational training - who might not have gone through a teacher-training qualification.
Independent schools have always been able to employ unqualified staff - and in 2012 a previous education secretary, Michael Gove, allowed academies more flexibility over unqualified staff.
This was to make it easier for schools to have lessons from people with particular skills, such as technology experts, sports tutors, musicians or linguists.
But it was opposed by teachers' unions who claimed it was a form of cost cutting and a lowering of professional standards.
Local authority schools still require teachers to have qualified teacher status, but there are exemptions such as specialist instructors, teachers trained overseas and trainee teachers.
Another former education secretary, Nicky Morgan, last year put forward plans that would have completely removed qualified teacher status.
But these proposals were reversed by the current Secretary of State for Education, Justine Greening, who has said she wants to strengthen QTS rather than end it.
"Some people have suggested that QTS might be scrapped or replaced with some vague notion of an 'accreditation'," she said in a speech earlier this year. "Let me be absolutely clear: not on my watch."
Ms Greening added: "Keeping and strengthening QTS is vital. This is not about removing school freedoms. But I believe that teachers should have the highest quality qualification and what I want to see is a QTS so well regarded, so strong that school leaders will naturally want all their teaching staff to have it.
"QTS should be the foundation stone for the teaching profession to build on."
A Department for Education spokesman said that unqualified teachers included "some trainees working towards their professional qualifications as well as experts, such as leading scientists, sports people or musicians, who head teachers think can add value to individual lessons and enrich the learning experience for children".