British Prime Minister Boris Johnson said Wednesday people born male should not compete in female sporting events, after a transgender cyclist was barred from a women's race.

Debate in Britain about transgender rights has become ever more acrimonious, and others in Johnson's government have said it should be left to sporting bodies to decide on who gets to compete.

But with splits emerging in both the Conservative and opposition Labour parties, ahead of local elections on May 5, Johnson went further in wading into the gender front of Britain's so-called "culture wars".

"I don't think that biological males should be competing in female sporting events. And maybe that's a controversial thing to say, but it just seems to me to be sensible," he told reporters.

"And I also happen to think that women should have spaces which are -- whether it's in hospitals or prisons or changing rooms or wherever -- which are dedicated to women," Johnson added.

His intervention came after the government last week was forced into an embarrassing U-turn, hours after a report said it planned to scrap legislation to ban "gay conversion therapy".

Following protests from Conservative MPs who back a ban, Johnson's government said it would persevere with the legislation -- but would exclude "transgender therapy", to allow counselling for teens seeking gender reassignment.

The flip-flop came a day after Conservative MP Jamie Wallis became the first British lawmaker to openly declare they were transgender, prompting messages of support from colleagues including Johnson.

The prime minister said he was "immensely sympathetic to people who want to change gender".

"We will have a ban on gay conversion therapy, which to me is utterly abhorrent," he stressed.

"But there are complexities and sensitivities when you move from the area of sexuality to the question of gender, and there I'm afraid there are things that I think still need to be to be worked out."

Last weekend, transgender cyclist Emily Bridges was barred from a women's race in England after the UCI, the sport's global governing body, ruled that she was ineligible.

The 21-year-old said she felt "harassed and demonised" after the UCI decision, which overruled clearance given to Bridges by British Cycling, the main governing body for the sport in the UK.

The initial decision to allow Bridges to race had caused major controversy, with threats of a boycott from other female riders if she was allowed to compete.

Critics say trans athletes have an unfair advantage even when testosterone levels have been lowered due to the impact of male puberty on the body.

The government's decision to exclude conversion therapy for transgender people from the forthcoming bill prompted its LGBT+ business envoy Iain Anderson to resign on Tuesday.

It also led to more than 100 charities and groups to pull out of the government's first international LGBT+ conference, due to take place in June, forcing the cancellation of the event.