The forecast is slightly worse than that of the previous Brexit deal struck by Theresa May | Justin Tallis/AFP via Getty Images Brexit deal would leave Wales-sized hole in UK economy, experts warn Economists say Boris Johnson’s ‘Brexit dividend’ does not exist.

LONDON — Boris Johnson’s Brexit deal would leave a hole in the U.K. economy the size of Wales, economists warned.

The agreement struck between the U.K. government and Brussels will leave gross domestic product 3.5 percent lower every year than if Britain remained an EU member, according to new analysis by the National Institute of Economic and Social Research (NIESR).

That amounts to a loss of £1,100 per person per year or £70 billion annually overall — roughly the size of the Welsh economy.

The deal would see the U.K. leave the EU single market and customs union, increasing trading barriers across the Irish Sea in the process, while aiming to sign Britain up to a free-trade agreement with the bloc later on.

Johnson has said quitting the EU would provide a “Brexit dividend” for Britain, but NIESR said no such dividend exists.

Arno Hantzsche, principal economist at the think tank, said it is a plus that the deal reduces the risk of a no-deal Brexit. But he said the agreement would still have a negative impact on the economy because it would “eliminate the possibility of a closer relationship” once the U.K. leaves the two major trading areas.

“It means that future trade will face significantly higher barriers both with goods and services,” he said. “And that means that we would not expect there to be a boost to the economy.

“In fact what we estimate is that in the long run the economy will be 3.5 to 4 percent smaller every year. This corresponds, in today's money, roughly to the size of Welsh economic output.”

The forecast is however only slightly worse than that of the deal struck by Theresa May, which NIESR said would leave national GDP 3 percent lower each year in the long run.

Analysis by the UK in a Changing Europe think tank this month estimated Johnson’s proposal could reduce GDP by between 2.3 percent and 7 percent in the long term compared with remaining in the EU. The government has refused to carry out its own analysis.

Hantzsche said the economic picture in Britain is being damaged by Brexit uncertainty, with the future outlook “contingent on the Brexit outcome” and the global slowdown in trade.

The NIESR analysis also found that the key free-trade agreements the British government hopes to strike with other countries would add 7.2 percent of GDP to the U.K. economy over a 10-15 year period, which Hantzsche said is a “marginal” benefit compared with the negative impacts of the deal.

But it found that there is a reduced chance of a recession, down from 30 percent to 15 percent, because a no-deal Brexit has become less likely.