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.