Philip Hammond should honour the Leave campaign’s pledge to spend an extra £350million a week on the NHS after Brexit, a senior Tory backbencher said yesterday.

Jacob Rees-Mogg called on the Chancellor to use next week’s Budget to set aside the extra cash from 2019.

He was speaking at the publication of a manifesto from the pro-Brexit group Economists for Free Trade (EFT), which said the Government can look forward to a windfall after the UK leaves the EU. It said Brexit will be ‘overwhelmingly positive’ for the British economy provided the Government adopts the right policies.

Mr Rees-Mogg called on the Chancellor to ‘meet the demands’ of Simon Stevens, the chief executive of NHS England, who called for the Leave campaign’s pledge to be met. ‘The challenge for the 2022 election is for the Tories to show that the NHS is safe in our hands,’ he said.

‘Although I did not want the £350million figure to be used, it was used – and the electors believed the promise was made. Politicians cannot and should not hide behind the small print. We promised £350million for the NHS – so we must deliver it.’

He suggested the Chancellor’s Budget should promise to meet the amount from 2019/20 – after we leave the EU.

The economist who wrote the report, Professor Patrick Minford, accused the Treasury of a ‘conspiracy of gloom’ that sought to undermine Brexit. Mr Rees-Mogg agreed – attacking the ‘false assumptions supplied by the Treasury’. He backed the report’s findings and called for a dramatic cut in corporation tax to 10 per cent by 2025 – or more quickly if the EU attempts to punish the UK by imposing tariff barriers.

The economists’ report concluded that the Government can look forward to a post-Brexit windfall of £135billion between 2020 and 2025, with a further £40billion a year from 2025. That includes £10billion a year saved by no longer having to pay into EU budgets. The EFT report said the priority for the Government should be to bring down trade barriers with the rest of the world.

The findings are sharply at odds with most mainstream economists, who have warned the UK faces lower growth and more pressure on the public finances as a result of the vote to leave.

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