Online betting volumes are expected to rocket ahead of Thursday's general election, as British punters turn to the political arena.

According to industry data based on the increase in betting around the 2015 election and last year's Brexit referendum, betting on political events is rising by nearly 10% year-on-year. Should the trend continue, online bookmakers may see betting volumes soar by as much as 40% tomorrow, compared to an average day.

Figures published by electronic payment provider Worldpay, found online betting volume was up by 30% on the day of the Brexit referendum, and turnover was also up by 32% compared to that of an average day.

Meanwhile, in the days leading up to the 2015 election, betting volumes were 21% higher than on average.

Betting on politics is now a massive business in Britain. Ladbrokes estimates some £30m will be gambled on the upcoming election in June - and the number of markets to bet on has grown exponentially from just a few years ago.

Betfair said almost £40m have been wagered across all General Election markets on Betfair Exchange and it estimates the figure to exceed a total of £60m, which would make it the third biggest political betting event in Betfair's history behind 2016 US Presidential Election and Brexit when £250m and £127m worth of bets were placed.

"In recent political events like the US Election and Brexit we saw vast amounts of money bet in the final few days, despite the fact that both Remain and Hilary Clinton were heavy odds-on favourites," said Betfair spokesperson Katie Baylis.

"Punters were no doubt encouraged by the closeness indicated by the polls and the uncertainty around the result right down to the wire."

The jump in wagers from the general election two years ago compared to Brexit last year, shows a growing market for political betting. The fact the polls have narrowed in recent weeks has also encouraged punters to bet on the outcome of the election, which seemed a foregone conclusion until last month.

"Now, as the polls begin to narrow, punters will be having a hard think about where the best returns lie and who could be the next prime minister," said James McGurn, vice president of digital content and gaming at Worldpay.

"With the spate of surprise results we've had recently, bookies could be in for the biggest day of political gambling to date."

According to the latest survey from Survation released on 6 June, the Conservative opinion poll lead over Labour has dropped by 16 points over the past month. The poll for Good Morning Britain, of more than 1,000 people between 2 and 3 June, put the Tories on 41.6% and Labour on 40.4%. A similar survey conducted by Survation between 5 and 6 May gave the Conservatives a 17 point lead over Labour.

Election betting graph
Labour have clawed back some ground in the polls but that has not been reflected in the betting market. Smarkets

However, while the polls have narrowed, the Conservatives remain clear favourites to be the ruling party for the next five years, with a weighted average of recent UK national polls showing the Tories retain a 43% to 37% lead over Labour.

Odds on the Conservatives winning the election fluctuate between 1/10 and 1/12, while odds on Jeremy Corbyn sweeping into Number 10 on Friday remain between 6/1 and 7/1. To put things into context, the odds on the British and Irish Lions winning their Test series in New Zealand are shorter.

Warren Gatland's men have got off to a shaky start in New Zealand, losing against the Blues after barely scraping past the Provincial Barbarians over the weekend, but remain 5/1 to win at least two Test against the All Blacks.

Betting exchange Smarkets believes the chances of the Conservatives to win most seats stand at 90%, with their chances of winning the overall majority only marginally lower at 79%, adding Labour has enjoyed a resurgence on the exchange platform in recent weeks, but not as much as polls suggest

Corbyn's lowest price - or longest odds - to be PM after the election was 4.5% but his odds have now more than tripled to 16% and he remains a better price than Brexit or Donald Trump were before votes began.