Rates of problem gambling may be more than eight times higher than previously thought, according to new data released by the betting industry regulator.

The Gambling Commission has previously said the proportion of people suffering from a gambling problem may be as low as 0.3% of adults in Great Britain.

The figure, which based on a telephone survey, has been latched on to by betting industry lobbyists as evidence that levels of harm associated with bookmakers and online casinos are relatively limited.

But on Thursday, the commission published “higher quality” figures, based on an updated methodology, that suggest that as many as 2.5% of the adult British population may be suffering from problem gambling.

That would equate to about 1.3 million people in Great Britain with a gambling problem, although the commission has yet to come up with its own population estimate and will use a larger survey conducted over a longer period of time in future.

Someone is defined as suffering from problem gambling based on the problem gambling severity index, which tallies their answers to questions such as whether they have borrowed money or sold possessions to bet, or whether they have run into financial trouble because of gambling.

The gambling minister, Stuart Andrew, said: “This new survey presents a higher quality picture of gambling participation and harm than has existed previously.”

Andrew is presiding over a government review of gambling regulation that is expected to result in tougher protection checks for players, new stake limits for online slot machines and a mandatory levy on betting firms to pay for treatment of addiction.

Carolyn Harris, the chair of a cross-parliamentary group of MPs examining gambling harm, said indications that problem gambling rates could be higher than thought were “no surprise”.

“I hope the industry will take note and will be as keen to use these figures as they have been to cite those that showed lower rates of addiction,” she said.

The commission said the procedure used to calculate the higher figure was “experimental”. However, it also said that it had finessed the methodology over three stages and expects to adopt it formally next year.

The correct way to measure problem gambling has been a source of regular disagreement between campaigners for reform and some sections of the industry.

The commission’s adoption of new, refined methodology could result in a significant and permanent rise in the headline problem gambling rate used by government in determining policy.

The regulator has previously relied on its own telephone surveys or separate health surveys conducted by each of the UK home nations.

The survey of 4,000 people by the commission, which was conducted over two months, also found that people were more likely to gamble in the hope of making money than they are because they have fun doing it.

In 2020, Kenny Alexander, then then Ladbrokes boss, told a select committee hearing: “Ninety-nine per cent of our customers will lose.”

But 38% of respondents to the commission’s survey said their reason for gambling was always “the chance to win big money”, while “making money” was the second most common answer, with 21%.

Only 16% of people said they always gambled for fun, while more than a quarter said having fun was never behind their decision to gamble.

The Betting & Gaming Council, the industry standards body that also lobbies on behalf of the sector, said the figures were experimental and remained “under evaluation”.

It pointed to a previous NHS survey that estimated problem gambling rates at 0.4%.

“The methodology used in this survey is different to previous surveys conducted by the Gambling Commission, so a different rate is to be expected,” said a spokesperson.