The U.K.'s former Prime Minister Gordon Brown told CNBC that he doesn't expect a closely-watched Brexit vote on Tuesday to go in the government's favor. "I don't think she's going to win it," Brown told CNBC on Monday, a day before British lawmakers were due to vote on Prime Minister Theresa May's deal to leave the European Union. May's "Withdrawal Agreement" faces deep opposition within the parliament and if her blueprint gets shot down, the consequences could be dire. Several potential scenarios could unfold: May's government could collapse; the U.K. could face a disorderly exit; a second referendum could happen; or the entire Brexit process may get scrapped altogether. According to Brown, May could even try for another vote in the near future.

I have not seen Britain more fractured than it is now. Gordon Brown Former Prime Minister of the U.K.

"If she loses the vote, then undoubtedly the opposition party will put down a vote of no-confidence in the government," the British politician told CNBC's Martin Soong at the UBS Wealth Insights conference in Singapore. But a no-confidence vote doesn't necessarily mean a general election, so May "is likely to come back and try to put her proposal, perhaps in an amended form, a few days later," he predicted. That could potentially lead to "a whole series of indicative votes" on different options for the country's future, he said. "There is a long way to go and sadly, this is a prolonged period of uncertainty both for investors and the economy but also for the political system." Failure to back Tuesday's deal "would be a catastrophic and unforgivable breach of trust in our democracy," May wrote in a Sunday Express editorial over the weekend. The vote was originally meant to take place in December but it was delayed on concerns of insufficient approval from the U.K. Parliament and May's Conservative Party, with disapproval from both Brexiteers and Remainers.

Former U.K. Prime Minister Gordon Brown Dan Kitwood/Getty Images

Why a second Brexit vote is needed

Brown — who was prime minister of the U.K. from 2007 to 2010, and served as chancellor under Tony Blair's government — believes a second referendum should happen. The country needed a period of nation-wide consultation after the first Brexit vote in 2016, not just a narrow parliamentary debate, he argued. "We've got to stand back, look at what's not been achievable under the parliamentary process we've got, and think again about how we can actually resolve this issue in the future." "I have not seen Britain more fractured than it is now," continued Brown, who is an advisor to Pimco, one of the world's largest money managers. He was recently hired by Swiss private equity firm Partners Group as an advisor.

Political risk a major fear