Celebrities have accused Rishi Sunak of showing "callous disregard" for delaying a ban on conversion therapy.
A letter, signed by stars including presenter Rylan Clark and Little Mix singer Jade Thirlwall, said the prime minister was "letting down survivors and victims of abuse across this country" by not committing to bringing in legislation on the issue.
Co-ordinated by LGBT+ campaigning charity Stonewall, the letter is also signed by actors Alan Cumming and Russell Tovey.
Conversion therapy is a process which tries to change someone's sexual orientation or gender identity. It can include talking therapies and prayer, however more extreme methods such as exorcism, physical violence and food deprivation are also used.
The Stonewall letter, addressed to Mr Sunak, states: "By letting the clock run out, you are showing callous disregard for the harm faced by LGBTQ+ people.
"You are giving the green light for abusers to continue unhindered. You are letting down survivors and victims of abuse across this country."
The letter also referenced a rise in hate crimes. According to the Home Office, in the year ending March 2023, police-recorded transgender hate crimes in England and Wales rose by 11%, to 4,732 offences.
The Stonewall letter says: "LGBTQ+ people deserve a government with the will to protect them from harm.
"This is the last chance for your government to keep one promise to our country's LGBTQ+ constituents.
"Please do the right thing and legislate for a complete ban on these horrific and life-altering practices."
Former prime minister Theresa May first promised to ban conversion practices in July 2018.
In March last year, then-PM Boris Johnson dropped plans for legislation, and later defended a decision not to include transgender people in a prospective ban by saying there were "complexities and sensitivities" to be worked through.
In January, the government said it would ban conversion therapy for "everyone", including transgender people.
Labour has also said it would introduce a "no loopholes" trans-inclusive ban on conversion therapy if elected.
Stuart Andrew, equalities minister, apologised last week for the delay on banning the practice, but did not commit to it being included in the King's Speech on 7 November.
When asked about the letter, the government described conversion therapy as "abhorrent" and said it was still "carefully considering this very complex issue".
Last month, the Equality and Human Rights Commission wrote to women and equalities minister Kemi Badenoch, insisting legislation to ban conversion therapy "is needed" and said it hoped it would be in the King's Speech.
A government spokesperson said: "No one in this country should be harmed or harassed for who they are and attempts at so-called 'conversion therapy' are abhorrent. That is why we are carefully considering this very complex issue."