Britons' incomes could be slashed by as much as 9.5 percent once the U.K. formally leaves the European Union, a new study released today by MIT economics professor John Van Reenen has claimed.

The report points to a 6.3 to 9.5 percent reduction in GDP per capita with the U.K. outside of the EU's single market on the basis that a one percent decline in trade reduces income per capita by between 0.5 and 0.75 percent.

According to per capita data from the World Bank and CNBC calculations verified by Van Reenen, this would make every U.K. citizen $4000 worse off. In 2015, U.K. GDP per capita stood at $43,875.97.

The EU accounts for approximately half of the U.K.'s trade deals. Van Reenen's paper suggests that countries outside the EU, even those within the European Free Trade Association, see trade with the bloc decrease by one quarter. As such, "a Brexit-induced trade reduction of 12.5 percent ... would reduce U.K. incomes by between 6.3 and 9.5 percent", says Van Reenen.



His estimates broadly align with the contribution the EU is thought to have made to the U.K. since joining the bloc in 1973. A recent study by Warwick University economics professor Nicholas Crafts concludes that EU membership has raised U.K. GDP per capita by 8.6 percent to 10.6 percent.

During campaigning for Britain's EU referendum, financiers New World Wealth (NWW) estimated that continued EU membership would cost Britons over $1,000 per year and claimed that life outside the Union would see individuals more than $20,000 richer by 2020.

Van Reenen's paper, the product of his time spent as director of the Centre for Economic Performance, slams euroskeptics and undermines British Prime Minister Theresa May's hopes for a 'Global Britain' with increased trading powers.

Speaking to CNBC Monday, the U.K.'s shadow secretary of state for trade and industry, Barry Gardiner, said that, under a new WTO agreement, the U.K. would have to increase exports to the rest of the world by at least 37 percent "just to stand still."

"Britain's GDP is less than one-fifth of the EU Single Market's GDP, it would have less bargaining power in trade negotiations than the EU does," notes Van Reenen.

"Under all plausible scenarios, Brexit will mean Britain is poorer outside than inside the European Union," he says, also pointing to the drop-off in foreign direct investment and skilled workers he expects to result from May's plans to regain control of the U.K.'s borders.

Van Reenen's paper also speaks to the growing swell of protectionist rhetoric in the West and fears over the potential demise of the Eurozone.

He claims that "those who favor protectionist policies are the ones who are most likely going to suffer from their enactment," and warns Americans who support President Donald Trump's tough stance on trade and immigration to "consider the likely after-effects of (Britain's exit) from the EU."

Van Reenen's is the latest forecast for the future of the U.K., which as yet remains unclear despite assurances laid out in a white paper last week stating that the U.K. will go ahead with a so-called 'Hard-Brexit'.

British MP John Redwood told CNBC last week that the U.K. would not suffer punitive tariffs or be made to pay a divorce settlement upon leaving the EU's single market, instead reaching a "perfectly amicable solution."

An Ipsos MORI poll released Sunday states that 58 percent of leaders of the 500 largest U.K. listed companies say Britain's vote to leave the EU has had a negative impact on their business.

