Stuart Adam, a senior economist at Institute for Fiscal Studies think tank, said increasing the annual income tax allowance to £20,000 could cost between £50bn and £80bn a year, depending on the details.

“As it stands, I don’t think they’ve really set out how they would pay for such big giveaways,” he said.

“Of course they don’t have to do that yet – we’re not at a general election. But at some point, if they’re going to be a party of government, they would have to make those numbers add up.”

Stuart Adam (on Reform’s fantasy tax cuts) via BBC