A U.K. vote to leave the European Union on June 23 would cause major currency fluctuations and dent growth in the country, according to Ramin Nakisa, global macro strategist at UBS.
He estimated it would have an approximately "2 percent impact on GDP (gross domestic product) in the U.K. over the long term." However, the "biggest effect would be on FX (foreign exchange), so we're saying euro/sterling would go to parity if there was an exit," he told CNBC Friday.
The euro would not come out unscathed, and growth in Europe would also be impacted, added Nakisa.
The euro-sterling cross was trading at around the 0.7636 on Friday morning and the single currency has slowly risen against the pound this year on fears of a so-called "Brexit".
Mike Amey, managing director and portfolio manager at Pimco, also told CNBC Friday that the currency was under pressure from the "Brexit" uncertainty. Pimco sees a 10 percent devaluation of sterling versus the dollar if Britain votes to leave the EU, Amey told CNBC.
Meanwhile, Nakisa believes the biggest risk of a "Brexit" vote would be "the negative current account … if you depend on other people to invest in your country and buy your bonds, then there's the risk that there'll be a sudden stop."
"People would stop investing and then the stabilization would have to come through currency so what we're talking about is a 30 percent devaluation of sterling on a trade-weighted basis," he said.
Nakisa made his comments on the same day that U.K. Prime Minister David Cameron addressed the G-7 summit, saying that the U.K. should "listen to our friends," after world leaders at the summit in Japan said "Brexit" would bring a "serious risk to growth."
Amey told CNBC that Pimco currently sees a 40 percent chance of the U.K. voting to leave the EU.
"People will vote with their wallet when it comes down to things," but there is a "non-trivial chance that the 'Brexit' vote gets derailed by the immigration situation or the terrorist threat."