LEEDS, England — Rishi Sunak’s gamble was a considerable one. Five weeks ago, the British prime minister bet the house on his belief that a summer election might offer his Conservative Party a better chance of holding onto power than waiting until the fall.

Calling a snap election served as Sunak’s last roll of the dice. But it has since emerged that in the days before he stood forlornly in the pouring rain May 22 and told the country he was going to the polls, a number of colleagues and underlings were placing bets of the more literal kind.

Reviewing data from the week before Sunak’s announcement, bookmakers noticed a spike in bets being placed on the election date. The amounts being staked were small — totaling just a few thousand pounds — but the sudden frenzy of activity was enough to warrant further investigation.

The question of whether these bets were being made by political officials, using insider knowledge of Sunak’s intentions to make a quick profit, has come to dominate what could be the Conservatives’ final days in power. It also encapsulates how some parts of the electorate perceive the party that has governed Britain for 14 years.

“The whole thing has reinforced the public’s prior concerns,” said Luke Tryl, executive director of More in Common, a research group. “It gets right to the heart of it: ‘One rule for them, and one rule for everyone else.’ ”

Craig Williams, one of Sunak’s key parliamentary aides and a Conservative candidate running for office, was the first to come under scrutiny after The Guardian reported that he had placed a bet on a July election May 19, three days before the prime minister’s announcement. Now suspended from the campaign, he has admitted to an “error of judgment” but not a criminal offense.

As the Gambling Commission, the regulator that oversees Britain’s rich and varied betting industry, extended its inquiry, a number of other senior Conservative staffers were named as being under investigation.

They included Tony Lee, the party’s director of campaigns, and his wife, Laura Saunders, a prospective Conservative candidate in the forthcoming election who has since been suspended by the party.

Rumors are swirling that a number of other Conservative staffers may soon be identified by the inquiry.

One of the officers protecting Sunak, meanwhile, has been arrested over allegations that he had also made bets on the timing of the election, and the Metropolitan Police has confirmed it is investigating a number of other law enforcement officials.

The scandal is yet another blow for Sunak as he campaigns less to win the election, scheduled for Thursday, than to staunch his party’s potential losses.

He had already caused an uproar after he left the 80th anniversary of D-Day commemorations early to conduct a television interview, a decision he later apologized for profusely. He then faced widespread mockery after claiming that he had known hardship as a child because his parents had not allowed him to have satellite television.

The gambling allegations have compounded that damage, polling experts said, adding to a sense of an out-of-touch party that appeared to consider itself above ethical concerns.

What was potentially most corrosive was “the perception that we operate outside the rules we set for others,” Michael Gove, one of the Conservatives’ highest-profile lawmakers, told The Sunday Times. “That was damaging at the time of Partygate,” he said, referring to the scandal over lockdown-breaking parties held inside then-Prime Minister Boris Johnson’s Downing Street during the pandemic, “and it is damaging here.”

Political betting is a growing industry, but markets on when elections might be called are, insiders say, inherently niche.

They are run, effectively, as novelties, designed to attract publicity and hopefully new customers, according to one long-standing political betting expert, who asked to remain anonymous because of the sensitivity of the industry.

They are not designed, he said, to generate vast returns. Bookmakers aim simply not to lose money on them, working on the assumption that there will be people — not just lawmakers but various party apparatchiks — who have access to better information than them. To restrict their losses, they limit the amount of money anyone can bet.

The bets made in the days just before Sunak’s announcement fit that bill. Williams, for example, is accused of wagering just 100 pounds ($125), for winnings that would have stretched to just a few hundred pounds.

The election scandal has resonated with voters not because they disapprove of all gambling, experts said, but because of what it suggested about the ethics of the governing party.

The extent to which it has cut through to ordinary people is breathtaking, according to Tryl. Its data suggests that the betting scandal, along with Sunak’s “gaffes” concerning D-Day and his comments about TV, have become the defining topics of the campaign.

The allegations have not made much difference in the polls, but that should be scant relief for the Conservatives, Tryl said, because it did not reflect how little the public cares, but how much of the electorate had already turned against his party. “A lot of people had already gone,” he said.

That, certainly, is the bookmakers’ view: The Conservatives are currently 70/ 1 to retain power.