chat service for sports fans. “If you use that data in a way that you know, or should know, is harmful to your users, then that’s a serious problem.”

Mr. Naik, who previously helped uncover data misuse by the political consulting firm Cambridge Analytica, was contacted last year by Gregg, who was seeking help getting copies of data from Sky Bet and companies it used to profile users.

The data that he and Mr. Naik obtained included a 34-page breakdown of his financial history from a company called CallCredit, which conducts fraud and identify checks for Sky Bet. It contained information about his bank accounts, debts and mortgage, with details down to monthly payments. In bold was a loan default in March 2019.

Another company used by Sky Bet, Iovation, provided a spreadsheet with nearly 19,000 fields of data, including identification numbers for devices that Gregg used to make deposits to his gambling account and network information about where they were made from.

A document from Signal, a company used by Sky Bet that provides tools for tracking users online and offline, listed personal characteristics, like Gregg’s history of playing slots and making soccer his favorite sport to bet on.

totaled $7.3 billion, nearly double the next-largest market, Japan, according to Global Betting and Gaming Consultants, an industry research group. This week, four of the top five free sports apps on Apple’s App Store in Britain are gambling related. The companies own and sponsor soccer teams and dominate advertising during televised sporting events.

The country is at the center of the global debate about regulating the new generation of betting apps. The government has opened a review of gambling laws that will include the consideration of new rules for data use and affordability checks, according to the agency conducting the review.

Lawmakers should pass new regulations that allow companies to use data to spot problem gamblers but limit how it can be used for marketing and other sales objectives, said James Noyes, a senior fellow at the Social Market Foundation, a London think tank.

“They detect your pattern of play, your likes, dislikes, spending tendencies and exposure to risk,” Mr. Noyes said. “It’s taking information about you and turning it right back on you.”

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