Businesses that employ foreign workers will be among the worst hit by Brexit, according to research from academic think tank The UK in a Changing Europe.
The report suggests that skilled immigration increases productivity, with a rise in the skilled migrant share of 1 percentage point linked to a productivity boost of 2%.
However, a net fall in skilled migration of about 60,000 - equal to about 0.2% of the full-time workforce in the UK - is estimated to hit GDP by up to 1.8% post-Brexit.
Separate research from the Office for National Statistics shows this has already started to take effect, as the number of EU nationals working in the UK fell by 132,000 over the past year.
The House of Commons is set to vote on the Brexit deal negotiated by Prime Minister Theresa May on 11 December 2018.
Professor Jonathan Portes, senior fellow at The UK in a Changing Europe, said:
"The Brexit deal would leave us in a customs union with the EU for the indefinite future - but it is a long way from frictionless trade.
"The additional trade barriers, combined with reductions in both skilled and unskilled migration from the ending of free movement, would leave the UK significantly smaller than it would otherwise have been over the medium to long term."
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