Rishi Sunak said the new wave of teachers’ strikes would be “enormously damaging” to children, insisting the pay offer rejected by the NEU on Monday was “very reasonable”.

Teachers are set to walk out on April 27 and May 2 after 98 per cent of National Education Union members rejected the offer it described as “insulting”.

But the Prime Minister told broadcasters he was “extremely disappointed with the actions of the NEU teaching union”, adding that the union had been offered a new pay deal “worth about 8 per cent on average”.

He said: “In spite of all of that…the NEU has rejected that and announced new strike dates which will be enormously damaging to our children, whose education has already suffered in the face of Covid.”

But Mr Sunak refused to say if a £1000 one off payment for teachers would now be withdrawn following the NEU rejection, saying only: “We have made a very reasonable pay offer.”

More than 191,000 teachers in England had voted against Education Secretary Gillian Keegan’s offer, the NEU announced at its annual conference in Harrogate today. Delegates broke into chants of “come on Gill, pay the bill”.

Most teachers in England have had a five per cent pay rise this year.

The Government had proposed an additional one-off £1,000 payment and an average 4.5 per cent rise for most staff in the next school year.

It had also pledged to create a taskforce to help reduce teacher workload. Dr Mary Bousted and Kevin Courtney, joint general secretaries of the NEU, said: “We have today written to the Education Secretary informing her of the next two days of strike action on April 27 and May 2 that NEU teacher members in England will now be taking.”

The action will be a blow for children who have already had their education disrupted by a total of seven days of strikes by NEU members this year, including four days in London schools.

Dr Bousted and Mr Courtney said the union would work to ensure pupils in Years 11 and 13 — crucial exam years — have a “full programme of education” on strike days.

Downing Street said it was “extremely disappointed” with the NEU’s decision to back more strikes, saying it would add to the disruption children have faced in school over the past few years.

The Prime Minister’s official spokesman said: “With a week of classroom time already lost and exams fast approaching it is extremely disappointing the NEU have called for more strike action. That decision will also result in less money for teachers this year with the independent pay review body looking at pay for next year only whereas with the government’s deal they could have had an extra £1000 in their pay packet.

“We continue to call on the NEU given the level of disruption children have already seen in recent years to their education to not take strike action. We have put forward a funded pay offer which we think is fair and proportionate. The NEU membership have voted against it …now it falls to the pay review body process in setting pay for next year.”

Asked if the Government would return with a revised offer, the spokesman added that there were “no plans to do that”. He said: “We remain open to further discussions but we felt this was a fair and reasonable offer.”

Ms Keegan described the ballot result as “extremely disappointing” and said the Government had negotiated “in good faith”.

Dr Bousted and Mr Courtney told conference delegates that the offer showed an “astounding lack of judgment and understanding of the desperate situation in the education system”.

They said: “No teacher wants to be on strike. Nor can they accept this offer that does nothing to address the decades of below inflation pay increases making them the worst paid teachers in the UK.

“The offer will do nothing to stem the teacher recruitment and retention crisis which is so damaging to our children and young people’s education. The Education Secretary has united the profession in its outrage at this insulting pay offer.”

In a message to parents, they also said the union did not want to disrupt education, adding: “Our action is aimed at getting the Government to invest in the education of this generation of children and the people who teach them.”

Responding to the announcement, the Education Secretary said: “After costing children almost a week of time in the classroom and with exams fast approaching, it is extremely disappointing that the NEU have called more strike action.

“Following a week negotiating in good faith, the Government offered teachers a £1,000 payment on top of this year’s pay rise, a commitment to significantly cut workload, and a headline pay increase of 4.5 per cent for next year — above both inflation and average earnings growth.

The offer was funded, including major new investment of over half a billion pounds, in addition to the record funding already planned for school budgets.

“Pay will now be decided by the independent pay review body which will recommend pay rises for next year.”

It comes as Louise Atkinson, the president of the NEU, today told members that she had organised her first strike at the age of nine. She said: “I encouraged the girls in my class to refuse to go back in after lunch, instead sitting on the goal line in protest at the fact that we were not allowed to play football.”

Ms Atkinson also attacked Ofsted, saying that the schools watchdog was the “driver for so much that is wrong in our schools and colleges”.