About 50 Tory MPs could force the government to toughen up its ban on conversion practices by backing a move to extend the protections to transgender people, the Guardian has been told.

Campaigners fighting for Downing Street to commit to outlawing the controversial exercise said “the battle is definitely still on” and remained confident that No 10 would either be swayed or defeated in the remaining months.

Insiders said No 10 was warned on Monday that they “might still lose” if the prime minister, Boris Johnson, chose to stick to his decision to water down the long-promised ban on so-called conversion “therapy”, by excluding people from it who are questioning their gender.

The Government Equalities Office was also said to have estimated that if the protections for trans people were stripped out of the bill, about 50 Conservative MPs could vote to add it back in.

Johnson reneged on a commitment for the conversion practices ban to cover all those who are LGBT last week, but partially backtracked in the face of a huge backlash from some of his own MPs.

A government spokesperson blamed “the complexity of issues and need for further careful thought” on the decision to leave out transgender conversion practices while “separate work” is carried out.

The answer was given short shrift by those who have pushed for a ban on coercive or torturous practices designed to stop someone from reconsidering their gender or sexuality, given they said intricate work on the issue had been underway for years.

They also scoffed at the suggestion apparently made by No 10 earlier this week that a royal commission would be set up to examine the issue, suggesting this would delay dealing with it indefinitely.

Crispin Blunt, a Conservative MP and chair of the parliamentary group on global LGBTQ+ rights, said it was “disappointing that our prime minister has yet to fully appreciate the sensitivities and complexities around gender identity as well as sexuality”.

Another Tory backbencher, Elliot Colburn, said he was “extremely concerned” at the “incredibly poorly judged” decision to exclude protecting transgender people from the ban on conversion practices.

“Excluding anyone from the scope of the ban sends the wrong signals,” he said. “Many other countries and territories have managed to pass these bans, we need to do the same. Fuelling the fire and giving into some kind of culture war will benefit no one.”

Patrick Corrigan of Amnesty International UK said: “A ban on conversion therapy that excludes trans and non-binary people is not a real ban on conversion therapy. Human rights cannot be applied selectively.”

But some Conservatives are pleased Johnson has been swayed to take a softer approach on the issue, believing that conversion practices are already prohibited by existing laws or would be too hard to ban that they would end up unfairly targeting faith leaders or medical professionals.

Dominic Raab, the deputy prime minister, said on Wednesday that Johnson’s position was correct, and added: “We should be able to discuss these sensitive issues with mutual tolerance.”