A player has placed a record-breaking £1 million, or $1.29 million, bet on Democratic challenger Joe Biden to be the next US president on the world's largest online betting exchange.

The bet is the largest political bet ever placed on the UK's legal betting market Betfair Exchange. The second biggest betting event was in 2016 during the election when Betfair’s handle was $257 million (£199 million) before Donald Trump, beat Hillary Clinton.

If Biden wins, then the bettor, whose identity is not known, would win a £540,000 ($696,170) profit on top of getting the original £1 million wagers returned.

Betters on the exchange give Biden a 65% chance of winning, while Donald Trump’s chances have improved to 35% from 34%. Matthew Shaddick, Head of Politics Betting at Ladbrokes Coral Group, said it is estimated about one billion pounds would be wagered globally across the industry.

Americans are set to begin voting today with the first polls to be opened at 10:00 GMT in Vermont.