Proposals to reform gambling laws have been postponed for a fourth time amid turmoil at top of the Conservative party, sparking outrage from campaigners who warned the delay would cost lives.

Advisers to Boris Johnson concluded that a white paper, which was scheduled to go ahead next week, could not be published until a new leader of the Conservative party was elected to replace him as prime minister.

The latest of a series of delays comes amid a tussle between different Tory party factions over the content of the plans, multiple Whitehall sources said.

Pro-reform MPs, led by Iain Duncan Smith, had sought to persuade Boris Johnson that tough curbs could burnish his legacy and were hopeful of success after the white paper was scheduled for next Tuesday on Downing Street’s announcement “grid”.

But senior adviser David Canzini is understood to have told Johnson that he could not publish it as it would require legislation from his successor.

MPs voiced concern earlier this week that advisers with past ties to the gambling industry, including Canzini, might obstruct or dilute proposed reforms, such as affordability checks or a mandatory levy to fund addiction services.

On Wednesday ministers dropped plans to push through an online safety bill next week on similar grounds, leading to allegations of a vacuum at the heart of government.

It is the fourth time that the gambling white paper, the culmination of a review announced in 2019, has been shelved.

The delay means proposals will not be published until a new Tory leader is elected in September, at the earliest, and is a blow to those pushing for tougher reforms.

A spokesperson for Gambling With Lives, a charity set up by parents whose children took their own lives after a gambling addiction, voiced dismay at the latest postponement.

“Tens of thousands more people will be harmed and some will die as a result of this inexcusable delay.

“[Ministers] spent two years assessing evidence to develop a white paper, which we hear has been stopped by a single unelected official with links to the gambling industry. The next PM be warned – bereaved families will be knocking down the door and demanding rapid reform when they take office in September.”

Duncan Smith, who has previously said he is ready to “go to war” with the government to secure tougher reforms, said he was “very sorry” that the white paper would be delayed.

“It wasn’t perfect, but I’d have accepted it because it’s an advance on where we’ve been,” he said.

Duncan Smith is backing Liz Truss to lead the Conservative party. He said she was “keen to do something” on gambling, but “I don’t know about Rishi [Sunak]” – referring to the former chancellor and leadership race frontrunner.

“The Treasury has pushed back on any of these changes so far and I’ve not talked to the others, who haven’t expressed a strong view,” Duncan Smith added.

He said that whoever became prime minister would “find me sitting on the couch in their study until they do it”.

The Labour MP Carolyn Harris, who chairs a cross-party group of MPs examining gambling harm, said: “This was a golden opportunity for the PM to bow out having at least done one good thing during his time in office.

“But it seems like those who influence his thinking are far more interested in protecting the online gambling industry than they are in fulfilling a commitment in the Tory 2019 manifesto.”

“This is a low, senseless and cruel blow for campaigners of reform.”

The gambling white paper falls under the auspices of the Department for Digital, Culture, Media and Sport. Damian Collins is the minister in charge of both technology and gambling at the department, after the departure of Chris Philp, a former Johnson loyalist who oversaw the white paper but was among the ministers whose resignation helped force the prime minister to stand down. His resignation letter urged Johnson to publish the white paper in its “full and undiluted” form.