Leading education union figures have joined forces to demand a 5 per cent pay rise for teachers from 2018, just weeks before the chancellor is due to deliver his budget.

In an open letter to the education secretary Justine Greening, the heads of six major unions expressed “grave concerns about the state of teacher supply” and demanded a significant salary bump for all teachers from next year.

The letter is signed by Geoff Barton of the Association of School and College Leaders, Paul Whiteman of the National Association of Head Teachers, Elaine Edwards of the Welsh union UCAC, Deborah Lawson of Voice, and Mary Bousted and Kevin Courtney of the National Education Union.

The letter echoes fears raised by the School Teachers’ Review Body (STRB) that low pay is making it more difficult to recruit and retain teachers, or encourage the best staff to apply for leadership positions, and warns of a “brewing crisis” in the education sector.

It points out that teachers have suffered seven years of real-terms pay cuts due to the government’s policy on public sector pay, and warns that teachers are paid less than other graduate professionals whether they are early in their careers or experienced school leaders.

“The situation is now so critical that it requires firm and decisive action,” the unions tell Greening. “In order to support and secure recruitment and retention, teachers’ pay levels must be restored to at least the levels that existed before the start of the pay restraint in 2010.

“We believe that teachers must be given an immediate pay rise of five per cent in 2018 as step towards this.”

The STRB has been told it will be given “flexibility” over the 1 per cent, but there are concerns that schools will not be able to afford even a small rise in pay.

Philip Hammond, the chancellor, will deliver the autumn budget on November 22, and the unions want to see cash allocated so schools can award a larger pay rise.

Their letter warns that 88 per cent of schools in England face further real-terms cuts, and urges the government to commit to a national framework of pay and conditions for all education staff in publicly funded schools to “ensure consistency, fairness and transparency”.