Emily Bridges previously set a national junior men's record over 25 miles and was selected to join British Cycling's senior academy in 2019UK Prime Minister Boris Johnson says he does not believe transgender women should compete in female sporting events - a view he conceded may be "controversial".
The issue of transgender athletes - centred around the balance of inclusion, sporting fairness and safety in women's sport - has recently focused on the case of transgender cyclist Emily Bridges.
Bridges was recently ruled ineligible to compete in her first elite women's race by cycling's world governing body.
Johnson was speaking on a range of issues, including the government's approach to the ban on so-called conversion therapy, before adding: "I don't think biological males should be competing in female sporting events. Maybe that's a controversial thing to say, but it just seems to me to be sensible.
"I also happen to think that women should have spaces - whether it's in hospitals, prison or changing rooms - which are dedicated to women. That's as far as my thinking has developed on this issue.
"If that puts me in conflict with some others, then we have got to work it all out. It doesn't mean I'm not immensely sympathetic to people who want to change gender, to transition and it's vital we give people the maximum love and support in making those decisions.
"These are complex issues and they can't be solved with one swift, easy piece of legislation. It takes a lot of thought to get this right."
What happened in the Emily Bridges case?
Bridges, 21, had been set to face some of the sport's biggest names at the National Omnium Championships in Derby last weekend.
She came out as transgenderexternal-link in October 2020 and began hormone therapy in 2021 as part of her gender dysphoria treatment - and had been allowed to enter women's events by British Cycling because of lowered levels of testosterone.
British Cycling's transgender regulations require riders to have had testosterone levels below five nanomoles per litre for a 12-month period prior to competition.
However, the UCI has not yet completed its own process around Bridges' eligibility to race in international competitions - meaning she could not participate.
In May 2021 - while still transitioning and racing in male events - she finished 43rd out of 45 riders in the elite men's criterium at the Loughborough Cycling Festival and in September she was second to last in the Welsh National Championship road race, a 12km lap behind the winner.
Last month, Bridges won a men's points race at the British Universities Championships in Glasgow - her final men's race.
Following the UCI decision, British Cycling said it "fully recognises her disappointment" but called for "a coalition" across a number of sports - involving governing bodies, athletes, the transgender and non-binary athlete community and the government - to work together to "find a better answer" in a way which "maintains the dignity and respect of all athletes".
British Cycling added: "We also understand that, in elite sports, the concept of fairness is essential.
"Transgender and non-binary inclusion is bigger than one race and one athlete - it is a challenge for all elite sports."
On the eve of the UCI's decision on Bridges eligibility, UCI president David Lappartient told BBC Sport he was "worried" transgender athletes could affect the fairness of competition in cycling, and said current rules based on testosterone levels were "probably not enough".
Lappartient said world cycling's governing body "fully recognises the rights of transgender athletes to do sport".
He added: "When I speak with some professors in medicine, some specialists, they say, 'yes your body probably has a memory already of what you are and so there is maybe some advantages'. Is it a bridge of fair competition?
"The question of fair competition is really a question we must put on the table and is it right to take part - when you do transition - at the highest level? Or do we have also to see if this affects the fairness of competition.
"I can also really understand some ladies saying: 'OK but we don't accept this'. And today I also [have] the union of the women's riders completely against this and challenging the UCI on this.
"So we are in between and we were challenged on all parts."
What are the current rules?
The most recent IOC guidance - updated in November 2021 after the Tokyo Olympics - said there should be no assumption that a transgender athlete automatically has an unfair advantage in female events.
It recommended that individual sports under the Olympic umbrella - such as athletics, weightlifting, gymnastics and swimming - make their own rules surrounding transgender athletes.
World Athletics has set five nanomoles per litre as its benchmark, with cycling set at below five nanomoles.
World Rugby has banned trans women from playing at elite level, while the Rugby Football Union's domestic policy in England does allow trans women to play, under certain testosterone-based conditions.
However, the IOC guidelines have been criticised by some medical experts, 38 of whom signed a statement questioning the changes made to its policy around testosterone suppressants in transgender women.
The sporting body said relying on testosterone levels alone in female events was no longer deemed sufficient grounds to determine whether or not a competitor has an unfair advantage.
But some medical professionals said the guidance was drafted mainly from a human rights perspective with little consideration of medical and scientific issues.
There has also been new guidance around transgender inclusion in non-elite sport, created in 2021. It was published after an 18-month consultation and review of the existing research and was developed by Sport England, Sport Scotland, Sport Northern Ireland, Sport Wales and UK Sport.
It said that "for many sports, the inclusion of transgender people, fairness and safety cannot co-exist in a single competitive model".
The report concluded that "testosterone suppression is unlikely to guarantee fairness between transgender women and natal females in gender-affected sports" and there are "retained differences in strength, stamina and physique between the average woman compared with the average transgender woman or non-binary person registered male at birth".
It challenged sport bodies to "think in innovative and creative ways to ensure nobody is left out", and stipulates individual sports may need to choose between inclusion or "competitive fairness" - and safety if relevant.
The guidance suggests for those sports where safety or fairness could be compromised, the individual sports could create an "open" or "universal" category separate to male and female ones.
More follows.
