Senior Conservative MPs have accused the government of a “moral failing” for delaying the long-promised ban on conversion practices that they say damage the lives of LGBT+ people. In a letter to Rishi Sunak, a cross-party group of politicians and campaigners criticised the slow progress in bringing forward new legislation since the pledge was made five years ago. The increased pressure on the prime minister and his equalities minister, Kemi Badenoch, came amid further wrangling over the contents of advice to schools on how to deal with pupils questioning their gender. The advice was planned for release before the end of the summer term. However, there is still concern among some Tory MPs over whether schools should be forced in all cases to inform parents if a child reveals they are questioning their gender. Sources close to Badenoch and the education secretary, Gillian Keegan, insisted there was no split between the pair. But Downing Street sought to distance itself from suggestions the hold-up was down to Sunak, and denied a final version had reached his desk. Both issues are thorny for the prime minister as he tries to limit Conservative splits by keeping the socially liberal wing of his party and those on the Christian right onside. After weeks of hoping by some Tory MPs that the conversion practices ban bill would be published, they broke cover days before the Commons summer recess to criticise the government’s continued failure to make good on its promise. The mooted plans for a ban on conversion practices are expected to cover sexual orientation and gender identity. However, those pushing for the strongest possible ban are concerned that exemptions for religious leaders and when consent is given could be inserted in the draft bill. Research published this year found that more than 400,000 people who are gay, transgender or non-binary had been subjected to someone trying to change, “cure” or suppress their sexual orientation or gender identity. In a letter to Sunak seen by the Guardian, those pushing for the ban to be enacted speedily said the government’s “moral failing” in not yet publishing the legislation “should concern us all”. They accused ministers of letting the UK lag behind other countries over such bans, and of seeking to “obfuscate and delay”. “Not only has the delay damaged the lives of countless vulnerable LGBT+ victims, it has also emboldened perpetrators to act with impunity,” said the group, which includes the equalities select committee chair, Caroline Nokes, and Elliot Colburn, a co-chair of the all-party parliamentary group on global LGBT+ rights. They added: “Protecting vulnerable people from abuse should be a primary aim of any democracy. We therefore urge you to fulfil your promise and publish the long-awaited legislation immediately. It is time to end these unethical, harmful and ineffective practices that have been condemned by religious leaders and by medical, psychiatric, psychological and healthcare professionals worldwide”. Other MPs from Labour, the Liberal Democrats and the SNP signed the joint letter, alongside campaigners including religious figures such as the bishops of Dorchester and Buckingham, medical professionals, academics and the chair of the Ban Conversion Therapy Coalition, Jayne Ozanne. Penny Mordaunt, the House of Commons leader, had said a special committee tasked with scrutinising a first draft of the conversion practices ban bill would complete its work by the end of the current parliamentary session. Though such work is meant to happen over 12 sitting weeks, Tory sources said that would be difficult given the looming summer and party conference recesses, before a new parliamentary session in the autumn. An Equality Hub spokesperson said: “This government is committed to protecting people at risk from conversion practices. As part of this we will publish a draft bill setting out our approach for pre-legislative scrutiny by a joint committee this parliamentary session. This will allow for in-depth analysis and challenge to test the policy and drafting and ensure we address any risk of unintended impacts.” Keegan refused to put a timeframe on when the guidance about transgender pupils would be published, saying on Monday only that it would be “in the near term”.