Whitehall sources indicated that the long-pledged ban will not be included in the King’s Speech on Tuesday – meaning it is unlikely to become law before the next general election.
Supporters of a ban argue that that “abhorrent” practice of attempting to change an individual’s sexual orientation or gender identity is damaging to LGBT+ people.
But Mr Sunak appears to have backed out his commitment to prohibit after intense lobbying by some of his MPs who argue a law could criminalise parents or teachers who give advice to children.
Elliot Colburn, a Tory MP who has campaigned for the practice to be outlawed, warned it is “not the end of the road” and threatened to take action in the Commons.
He said that rebels were considering a plan to amend different legislation, such as a law and order bill, to call for a ban to protect gay and transgender people. “We’re looking at every possible opportunity and we’re definitely not going to let this drop.”
“Not to deliver on it would be absolutely appalling,” said Mr Colburn. “The government had the opportunity to grab the bull by the horns and get this done. And now they’re essentially going to have to let parliament do it.”
Alicia Kearns, the Tory MP who chairs the foreign affairs committee, accused colleagues who oppose a ban of “imprisoning” LGBT+ people in a “cycle of imposed shame and self-hate as you reinforce bigotry”.
Tory colleague Dehenna Davison added: “It is shameful that, over five years after promising we would deliver a much-needed ban on conversion therapy, it now looks set to be kicked into the long grass.”
The former levelling up minister added: “How anyone can justify supporting such practices is beyond me.”
Mr Colburn believes a “massive majority” of the Tory party are on his side – but a group of right-wingers, including family values advocate Miriam Cates, have put pressure on No 10 to drop the legislation.
A letter to Mr Sunak warning that bringing forward a bill would be “extremely concerning” was said to have garnered more than 40 signatures after being sent to Tory MPs by Ms Cates.
A source in the right-wing, anti-ban camp said it would be a “brave move” for rebels to try to force through a law while relying on Labour votes.
There are suggestions that the legislation will be downgraded to a draft bill in the King’s Speech setting out a consultation on the issue in an attempt to soothe the anger of campaigners.
Jayne Ozanne, the former government adviser who now leads the Ban Conversion Therapy coalition, said she was “so angry” that the Tories appeared to be reneging on a firm promise to ban the practice.
“The Tory party will never be trusted by LGBT people, their friends and allies again,” she tweeted on X. “The moral failure to protect LGBT people takes us back to the 1980s.”
The Equality and Human Rights Commission wrote to women and equalities minister Kemi Badenoch last month to insist the ban is “needed” and should be in the speech setting out the government’s legislative priorities.
Theresa May first promised to eradicate the practice in 2018, before it was downgraded to not include transgender people by Boris Johnson. However, Mr Sunak’s government then said in January it would ban conversion therapy for “everyone”, including transgender people.
Labour has pledged to introduce a “no loopholes” trans-inclusive ban on conversion therapy. The government has described the practice as “abhorrent” but said it was “carefully considering this very complex issue”.