Betting companies now say Brexit will be the favourite by the weekend
William Hill's Leave odds are now 5/4, or a 44% chance, but it says that by the weekend the odds could well be even shorter, suggesting a Brexit is likely to happen.
Graham Sharpe, media relations director for William Hill, said the company was having to shorten Leave odds daily, and that the betting was only going in one direction:
"We were forced to shorten our Brexit odds yet again overnight," he said "and having once been long-odds outsiders at 9/2 (18%) the odds have now come all the way down to 6/4 (40%).
"The momentum is such that it seems inevitable Brexit will be favourite by the weekend if this trend continues"
He added that if betting translated into voting, Brexit would win by a landslide:
Remain was once 1/7 favourite (87.5% chance) but those odds inched down slowly, then over the last few days, as the Brexit betting bandwagon began to roll.
71.7% of all the bets we have taken since we first opened our book have been for Brexit, and if that were to be translated to voting patterns it would be all over.
Rival Ladbrokes seems to agree, also placing 5/4 odds on a Brexit - with even shorter odds likely to follow.
"The political environment in the past couple of days has seen a huge shift of bets towards the Leave campaign," Matthew Shaddick, head of political betting at Ladbrokes, said. "The odds are now at their shortest since we opened the book and it is being driven by English and Welsh bettors."
Ladbrokes has also placed short odds on a huge referendum turnout, with an 80% chance of over 60% of those eligible placing their vote.
Betfred, Paddy Power, Skybet and Betfair have also placed 5/4 odds on a vote for Brexit. Business Insider will keep readers updated on changing odds as they occur.
Online and telephone polls on Monday showed a surge in the Leave side, suggesting 53% would vote for a Brexit. The Sun - the UK's most read newspaper - also came out for a Brexit this morning. It has never called wrongly called a General Election.