Ex-CEO of oil giant says UK would 'probably never recover' from Brexit

Former BP CEO John Browne said Thursday the U.K. would likely never recover from leaving the European Union.

Browne spoke as Britons headed to the polls to vote on their future relations with the economic bloc.

"I will be holding my breath, but I believe that the common sense of the people of the U.K. will be to stay in the EU," Browne told CNBC. "The cost of uncertainty is high, and you know, you very rarely recover that cost."

"The uncertainty created by leaving would be so great, we'd probably never recover from it," he added.

Browne, a supporter of the remain camp, wrote in an op-ed in The Wall Street Journal earlier this week that polls showing an extremely tight race have created "perhaps the most worrying moment for the United Kingdom since World War II."

Polls leading up to the nonbinding referendum have swung both ways, with the latest numbers indicating a small lead in favor of remaining in the EU, after previously showing the leave option had a slight edge. Betting markets are putting their money on a lead for the remain vote.

Earlier in the day on CNBC, former European Central Bank President Jean-Claude Trichet expressed caution that there was no way to know in advance how the U.K. would vote, but said a win for leave would have large ramifications.

"It's absolutely clear for me as it is for the IMF, for [British Prime Minister] David Cameron, for the Bank of England, that there are enormous costs associated short term, medium term and long term associated with Brexit," Trichet said.

In his interview on CNBC, Browne said leave proponents were overstating how little independence the U.K. has. He also said leaving could open the doors to "a more nationalistic approach with bad consequences" across Europe.

Browne also said the uncertainty created by a leave vote would increase the cost of capital. He also addressed concerns about the impact of globalization on the U.K.'s economy.

"It's up to us to make that work for people and to stop the middle of all economies being hollowed out," Browne said.

Trichet acknowledged the challenges created by globalization, and said it is creating "some kind of anguish on our workers."