The National Education Union’s leadership has threatened to organise a huge protest during the Conservative party conference, accusing Gillian Keegan, the education secretary, of being deluded about teachers’ pay and staff shortages.

The NEU’s joint general secretary Kevin Courtney told delegates at the union’s annual conference: “If you need to, you will organise the biggest demo Manchester has seen for decades on 2 October, you’ll carry on a campaign right into the general election year. And you will win.

“The government is so rattled by our campaign, so rattled that it is reacting foolishly.”