IN WHAT may be one of the greatest political ironies of the 21st century, new analysis claims Brexit is costing the economy £350 million a week.

During the EU referendum the official Vote Leave campaign decked out a bus with the words “we send the EU £350m a week, let’s fund our NHS instead”.

This argument was dismissed as cobblers at the time, with the government’s official statistician raising concerns over the figure, but it was seen as being heavily influential.

Vote Leave director Dominic Cummings even said his side would likely not have won without the claim.

But research by the Financial Times suggests the value of Britain’s output is now around 0.9 per cent lower than it would likely have been if the UK had stayed in the EU – just under £350m a week.

An academic leading publicly funded research into the effects of Brexit, Jonathan Portes, professor of economics and public policy at King’s College London, told The National: “The conclusion that, very roughly, Brexit has already reduced UK growth by one per cent or slightly less seems clear.”

Since the vote, the pound has fallen in value by about 10 per cent while inflation has risen more in Britain than in other advanced economy, going from 0.4 per cent at the time of the referendum to 3.1 per cent last month.

A study by academic Thomas Sampson and some colleagues at the London School of Economics found that 1.7 per cent points of the 2.7 percentage-point rise in inflation over the past year is due to Brexit. Sampson calculates that “the Brexit vote has cost the average worker almost one week’s wages”.

In a worrying sign for Scotland, where there are effectively more jobs than workers able to work, net migration to the UK from the EU has fallen by 40 per cent in the first 12 months after the vote.

Already trade bodies are worried about the lack of staff in farming, food, and tourism.

But Tory Brexit champion Iain Duncan Smith said businesses will have “to learn to get by” with all the difficulties coming their way.

“l don’t buy this idea of a fixed position in the world,” he told BBC Radio 4’s Today programme. “It’s not a case of less trade, it’s a case of a different type of trade, and British business will have to learn, as they do, to get by in a different world.

“And bear in mind, we are looking to make trade arrangements which will make life easier for us with other markets. So, you have to look at these things no longer in a case of just the European Union.”

Duncan Smith added that leaving the EU would obviously lead to new barriers with the UK’s largest trading market.

“We are leaving so we won’t influence their future trade regulations,” he said.

Asked about Duncan Smith’s comments a spokesperson for the Prime Minister said yesterday that “we are looking for a deal that will have business at the centre of it. We will secure a deal that is in the interests of British businesses and the British people.”

The SNP’s Kirsty Blackman accused the veteran politician of “living in cloud cuckoo land” for dismissing the “huge threat that Brexit poses to the Scottish and UK economies.”

She added: “All the evidence shows that Theresa May’s extreme plans to drag Scotland and the UK out of the single market and customs union will cost hundreds of thousands of jobs, and hit people’s incomes, livelihoods, and living standards for decades to come.

“We already know the damaging impact that Brexit is having on the economy before we have even left the EU – as growth slumps, prices rise, wages are squeezed, and the UK gets ready to pay out billions of pounds to negotiate a trade deal that will inevitably be worse than the one we already have as an EU member.

“As we move into the critical second phase of the Brexit negotiations it is vital that we remain in the single market and customs union. Short of retaining our EU membership, that is by far the least damaging option, the best compromise, and the only way to protect jobs and the economy.”

Last year Duncan Smith’s colleague Liam Fox claimed the EU had allowed firms in Britain to become “too lazy and too fat” with businessmen preferring “golf on a Friday afternoon” to trying to boost the country’s prosperity.