Probability of a Remain vote in Britain's EU referendum soars to 78 percent: Betfair odds

William Hill said it was offering odds of 1/5, or an 83 percent chance, for a vote to Remain.

"It has not been unusual during the campaign to see sudden surges for one side or the other, and although the Monday money was mainly for Remain we still took a 5,000 pound bet for Leave," said William Hill spokesman Graham Sharpe.

Britain votes on whether to leave the EU on Thursday.

(Reporting by Guy Faulconbridge; editing by Stephen Addison)