British sports governing bodies are under mounting pressure to reform their policies after world swimming banned transgender athletes who reached male puberty from elite women’s events.

In a seismic move for Olympic sport which will mean that American swimmer Lia Thomas can no longer compete in elite races, swimming’s rulemakers announced that transgender women must now establish that they “have not experienced any part of male puberty”.

Fina, world swimming’s governing body, also announced plans to establish a new “open” category of competition to include transgender women that, according to president Husain Al-Musallam, would involve “some of our biggest events”.

Transgender men can still compete in the male swimming category and a working group will report back within six months on how a new open category could work for women who transitioned after puberty.

The move was immediately endorsed by the British Government, which wants domestic sports governing bodies to collectively form new policies.

British Cycling has suspended its domestic transgender inclusion policy pending a review and British Swimming must now decide whether to follow the rules that Fina has outlined for international competition.

“This is the right and sensible decision to take,” said Nadine Dorries, the Culture Secretary. “Fairness must always take precedent over inclusion and should be unequivocal. Also important that trans women are able to compete in own class, this is the solution.”

Al-Musallam said swimming’s new policy was “based on real science” and there is confidence it will prove robust against any legal challenge in being “necessary and proportionate to achieve a legitimate” objective. “Our athletes must come first,” he said. “Of course, I understand why transgender athletes would like to compete in a category of their choice. However, I have an obligation to every single one of our athletes.

“Equality is also a key principle for us. This is why we are faced with such a delicate balancing act. We have to protect competitive fairness, and also the past records and achievements.”

Although the policy could have been passed just by Fina’s executive bureau, endorsement was sought from national governing bodies at an extraordinary general congress in Budapest ahead of the World Swimming Championships.

More than 70 per cent of governing bodies agreed, with 15.3 per cent against, and 13.1 per cent who abstained.

Individual countries could still implement their own transgender policy for domestic competition, with the International Olympic Committee ruling last year that individual sports must establish their own frameworks.

The International Cycling Union (UCI) announced a new policy on Thursday, opting to allow transgender women to compete if they have gone through puberty provided their testosterone has been suppressed to below 2.5nmol per litre for at least two years. That would potentially mean Welsh cyclist Emily Bridges could still compete in women’s events at the Paris Olympics in 2024.

The UCI and British Cycling had allowed transgender riders to compete if their testosterone was continuously below 5nmol/l for a year but Bridges was barred shortly before the national track championships despite meeting those rules.

Bridges is adamant that her tests prove that she would have no advantage in races against women, while Thomas said she transitioned to “be true to myself” and that there was no threat to women’s sports.

Cycling’s decision to reduce its limit still faced a backlash from campaigners, who believe that crucial physical advantages remain after puberty even if testosterone has been suppressed.

In announcing its policy, Fina executive director Brent Nowicki said that “male to female transgender athletes, whose legal gender is female, may only compete in Fina competition and set world records in the female category, if they can establish that they have not experienced any part of male puberty”.

He added athletes would have to show they suppressed male puberty “beginning from tanner stage two or before the age of 12, whichever is later, and that they have since maintained their circulating testosterone below the levels of 2.5 nmol/l”.

Nowicki said that Fina had “consulted widely” and used “a team of leading experts in the fields of science, medicine and the law”.

British swimmer Sharron Davies, who was denied Olympic gold in 1980 by state-sponsored doping in East Germany, called on other sports to follow swimming’s lead.

“All the sports should be doing this,” she said. “I can’t tell you how proud I am of my sport for doing the science, asking the athletes/coaches, and standing up for fair sport. Biological females deserve the same opportunities of success in sport as their male counterparts.”