One gambler in the UK has bet 1 million British pounds ($1.29 million) through an online bookie on Joe Biden to become the next president.

It is the largest bet ever on an election and the third-largest on Betfair Exchange's platform.

Betfair, the world's largest online betting platform, said the U.S. elections are set to be the most-bet-upon event. It said it is expected to surpass most sporting events in terms of total bets. The company didn't identify the punter - but did say he placed the wager Oct. 29.

The bet stands to win 1.54 million pounds if Biden wins. As of Monday Betfair said that it has so far received 274 million pounds in bets on elections. The company expects that number to increase as it will allow players to continue placing bets until a winner is declared.

The 1 million pounds is currently the third-largest bet with the company behind a 1.1 million pound bet on tennis player Rafael Nadal in 2010 and the 1 million pounds bet on Floyd Mayweather Jr. in 2017.

Betfair said it expects bets to exceed 400 million pounds before the winner is announced. This would be around twice the amount placed in 2016

Apart from the U.S. elections, Betfair also took bets on other political decisions including on whether the UK would vote to remain in the European Union in 2016.

The second-largest bet ever made on an election was a 555,000-pound wager on Donald Trump in 2016.

The bet came a day after the election when almost all of the U.S. polls had closed. Bets usually take several days to be encoded into the system as the platform will need to place it against bets made for the opposing outcome. A single large bet could be placed against dozens of smaller bets before it gets validated.