Plans to prevent strikes by teachers’ unions from closing schools were included in a draft version of the Conservative Party manifesto for this year’s election, it has been reported.

The idea of reducing disruption caused by strikes in key public services was dropped after cabinet ministers said it would alienate teachers and other public sector workers, the Mail on Sunday said.

It quotes an email sent to the political campaigns company used by the Conservatives, dated 25 April and entitled “minimum service levels for strikes”, as saying: “Legislate to introduce minimum service levels in transport and other public services including border staff, prison staff, teachers, doctors and nurses in the event of a strike.”

The newspaper said this legislation would have forced staff working in key public services to maintain minimum levels of service during strikes, and would have made it easier for agency staff to break strikes.

The article also reported Tory aides as saying, after the plans were dropped from the manifesto, that the prime minister had hoped to introduce them after the election but had to abandon the idea after losing her majority.

Since the election, the government has confirmed there will be a 1 per cent cap on teachers’ pay this year, but has lifted the public sector pay cap for police and prison officers, and suggested there could be “flexibility” regarding teachers’ pay next year.

The government has already tightened the rules around strikes, with last year’s Trade Union Act requiring at least 50 per cent of a teacher union’s members to vote in a ballot and 40 per cent to say yes, for action to go ahead.

Last month, Mary Bousted, joint general secretary of the National Education Union, told Tes the new law did not rule out the possibility of strikes in the future.

She said: “I’m certainly not saying there won’t ever be national industrial action again. The issue would have to be absolutely critical and we would have to mobilise effectively.”

She said it was likely that the nature of industrial action would change, with an increase in “school-by-school action” where it is easier to achieve the thresholds.