The research, conducted by professional services firm PwC on behalf of business group the Confederation of British Industry (CBI), said on Monday that Brexit’s cost would pose a "serious shock" to the British economy by 2020 - equivalent to five percent of annual gross domestic product (GDP).

"This analysis shows very clearly why leaving the European Union would be a real blow for living standards, jobs and growth," said Carolyn Fairbairn, the director general of the CBI.

"Even in the best case this would cause a serious shock to the UK economy,” Fairbairn added.

According to the study, leaving the EU may raise the unemployment rate in the UK by 2-3 percent.

The Vote Leave campaign, which is in favor of an exit, refuted the study, with chief executive Matthew Elliott saying the CBI's scenarios were "skewed" and that Brexit was the "only safe option."

EU membership has long been a hot topic in Britain. Pro-Europeans warn that an exit could trigger the breakup of the UK by prompting another Scottish independence vote. However, Eurosceptics, who believe the UK would be better off outside the political and economic union, seek the UK's withdrawal from the EU.

British voters are scheduled to go to the polls on June 23 in a referendum to decide whether to leave the 28-nation bloc or stay in it. Recent opinion polls suggest that the voters remain sharply divided on the issue, with about 40 percent on either side and almost 20 percent still undecided.

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