The National Union of Teachers heard warnings of a "crisis" in schools struggling to recruit teachers.

Teachers warned of excessive workload and inadequate pay damaging both recruitment and retention.

A Department for Education spokesman said: "We're investing hundreds of millions in teacher recruitment."

The National Union of Teachers' conference in Brighton heard warnings about the recruitment problems facing schools. Christine Blower, the union's leader, described it as a "desperately serious situation".

"The causes of the retention problem are clear: workload, workload, workload - for not enough pay," said Ms Blower.

The conference backed a motion promising "support for members up to and including strike action" for any teachers facing worse conditions because of staff shortages.

Mark Taylor from Birmingham said he worked as a supply teacher and had been in schools where a third of staff were now supply teachers, because schools could not recruit full-time staff.

Paul Mcgarr from east London said teachers did not go into the profession for money, but the worsening quality of their working lives was driving people to leave.

There were also warnings that teachers' salaries had not kept up with rising costs, such as housing.

Ceinwen Hilton from Islington in north London said that for inner-city areas the price of housing was proving a "serious cause of hardship" for teachers.

The union conference highlighted teacher shortages and concerns about school funding as the "two most serious threats" to the quality of education.

Delegates backed calls to make teacher shortages a spending priority, rather than "diverting money to politically motivated policies" such as academies and free schools.

They also accused the changes to training routes into teaching as being "chaotic".

But the Department for Education rejected the claims, saying that there had already been substantial spending on recruitment and that school vacancies were not unusually high.

"We're investing hundreds of millions in teacher recruitment and the vacancy rate has remained low at around 1% over the last 15 years," said an education department spokesman.

"In fact, last year we recruited 116% of our primary schools target, and the pupil teacher ratio has remained stable when compared to 2010.

"We know unnecessary workload is one of the biggest frustrations for teachers and have done more than ever to tackle this by publishing the results of the three workload review groups on marking, planning and data collection - the three biggest concerns raised by teachers through the workload challenge - and accepting all their recommendations."