Johnson was hit by a torrent of ministerial resignations following the departures of chancellor of the exchequer Rishi Sunak and health secretary Sajid Javid from the cabinet the previous evening and Chris Philp, the minister with responsibility for gambling, became one of the latest to resign on Thursday morning.

Philp pointed to the impending gambling review in his resignation letter, writing: "The gambling review is with No 10 at the moment for final approval, containing strong measures to protect people from the ravages of gambling addiction.

"I have met with the families of those who have committed suicide as a result of gambling addiction, and I strongly urge you to deliver the review in full and undiluted."

Time had already been running short for the long-awaited white paper to be published before the summer recess, due to start on July 22, and the government's proposals for reform of gambling legislation may now not appear until the autumn.

The gambling review was launched in December 2020 with the aim of updating gambling legislation to make it "for the digital age".

It is set to contain plans to bring in controversial affordability checks on bettors, an area of concern for both punters and the British racing industry, with the last-named fearing the most hardline proposals advocated by campaigners could reduce the sport's revenues by tens of millions of pounds.

The Racing Post understands that a proposal contained in the white paper places the threshold for enhanced checks at a net loss of £2,000 over a 90-day period.

Should affordability checks require customers to provide personal financial information such as bank statements and wage slips, the betting industry believes the consequences on the levy would be a reduction of between £20 million and £30m, while Betting and Gaming Council chief executive Michael Dugher claimed the white paper could have a "drastic impact" on the funding of racing and should set "alarm bells ringing" for punters.

It is also understood that ministers intend to bring forward the timing of a review of the levy system to this autumn with the aim of the sport avoiding any unintended consequences from the white paper's proposals.

The Gambling Commission has already been accused of ramping up intrusive affordability checks for punters without having the necessary mandate.

On Wednesday Tim Miller, executive director of research and policy at the Gambling Commission, said that the industry regulator had been led to a "far more prescriptive regulation of customer interaction".

He told the CMS Gambling Conference in London: "Our preferred approach is and remains in favour of outcomes-based regulation and avoiding overly prescriptive rules and requirements. However, that preference is not sustainable where we consistently see a failure to achieve positive customer outcomes."

Miller added: "Our focus on customer interaction has been there for some time now and will certainly be continuing over the coming months.

"Both the commission and the government have stated publicly that more work is needed here, especially on how operators understand whether they are allowing customers to gamble in ways that are unaffordable. So a continuing focus on this should come as no surprise to anyone."

by Bill Barber