In late March, the Prime Minister dropped plans to ban any conversion therapy, but U-turned within hours following a backlash.
The Government later outlined legislation – the Conversion Therapy Bill – in the Queen’s Speech which would ban conversion therapy intended to change someone’s sexual orientation in certain scenarios.
But it said that, due to the “complexity of issues and need for further careful thought”, the legislation would not ban transgender conversion therapy.
Writing in the i for the 50th anniversary of the UK’s first Pride, Mrs May said: “Few people, reading of accounts from trans people, would disagree that they still face indignities and prejudice, when they deserve understanding and respect.
“We need to strive for greater understanding on both sides of the debate. Just because an issue is controversial, that doesn’t mean we can avoid addressing it.
“To that end, the Government must keep to its commitment to consider the issue of transgender conversion therapy.
“If it is not to be in the upcoming Bill, then the matter must not be allowed to slide.”
Mrs May said she regretted her past opposition to LGBT equality, having voted against reducing the age of consent for homosexual acts in 1998 and against the repeal of section 28 in 2002.
She said that, 50 years after campaigners were subject to abuse and ridicule, “we can take pride in how much, and how profoundly, attitudes have changed”.
“I include myself in that – looking back now, there are issues I would have voted on differently, were I to vote on them today,” she added.
The Prime Minister also wrote for the paper to commemorate the anniversary, and said it gave him the “greatest pride to lead a country where you can love whomever you choose to love”.
Mrs May’s statement comes after a Scottish Conservative MSP criticised the Government for excluding transgender people from the proposed ban, branding the move as “indefensible”.
Speaking at a PinkNews reception at the Scottish Parliament in Edinburgh on Wednesday evening, Jamie Greene MSP for West Scotland hit out at comments made by Boris Johnson towards trans women.
Mr Greene said: “I’m not a member of the UK Government first of all – I want to make that clear – and it’s not my job to defend the indefensible.”
He said the Conservatives had made a “very explicit” commitment to include trans people in the ban, adding: “We made a commitment to the LGBTQ+ community that we would ban conversion therapy. We should fulfil that promise and the Scottish Government should do exactly the same.
“We should do it here, we should do it in Westminster, we should do it in Wales, we should do it in Northern Ireland.”