The Conservatives are preparing to offer millions of workers a tax cut worth up to £460. Ministers are drawing up plans to raise the threshold at which employees begin paying National Insurance, in a move previously described by economists as the most effective tax cut for lower earners.

The pledge is being discussed as a possible centrepiece of a manifesto designed to win over blue collar voters, particularly in the Midlands and the North, considering voting for the Conservatives for the first time.

The disclosure comes after Andrea Leadsom, the Business Secretary, signalled in an interview with The Telegraph that the Tories were preparing to launch a manifesto that would commit the party to tax cuts. “A Conservative government will always be a tax-cutting government," Mrs Leadsom said.

Mr Johnson signalled his interest in reducing national insurance payments during the Conservative leadership contest after his rival Dominic Raab, now the Foreign Secretary, said that he would raise the threshold at which workers start paying the tax, from £8,632 per year to £12,500, matching the starting point for income tax.