Betfair Doubles Probability of Brexit

The chances of the UK leaving the European Union have almost doubled in just three months, if the odds from Betfair Group Plc's gambling exchange are any indication of sentiment.

The probability of a majority vote for leaving the EU has jumped to 36 percent, from 18.5 percent at the end of July, based on the odds given to bettors on the outcome of the referendum.

While bettors are following the momentum of the polls, it would require a huge swing for so-called Brexit to become the favorite outcome.

"A vote in favor of staying in the EU is still the firm favorite at 1.56 (4/7 or a 64% chance), in much the same way as the Scottish Referendum market was predicting a No to independence from very early on," Betfair spokeswoman Naomi Totten said by e-mail. "The price for a vote in favor of leaving the EU is the shortest it has been since June, currently trading at 2.76 (7/4 or a 36% chance), but in the context of the market it is still very much assumed that Britain will vote to remain within the EU."

UK Prime Minster David Cameron has said a referendum on Britain's membership will be held by the end of 2017 - though a date hasn't been set yet. The Conservative government wants the U.K. to stay part of a reformed EU and is currently in negotiations with regional leaders to secure chances before the vote.