Campaigners say there are "no excuses" for allowing transgender women to compete in women's sports events, after a landmark legal decision in Britain on Wednesday.

The Supreme Court, the UK's highest court, ruled that the legal definition of a "woman" is based on a person's sex at birth and does not include transgender women who hold a gender recognition certificate.

The decision is a significant victory for gender-critical rights campaigners and could have implications for participation criteria related to women's sport.

Fiona McAnena, director of campaigns at the charity Sex Matters, welcomed the ruling, saying it was crucial for fairness and safety.

"There are now no excuses for sports governing bodies that are still letting trans-identifying men into the women's category," she told the PA news agency.

"The judges mentioned fairness in sport this morning. The law was always clear that everyone male can be excluded to provide fair, safe sport for women and girls, but some people claimed it was unkind or complicated to do so.

"It's neither of those – it's essential for fairness and safety for everyone female."

Transgender participation has become a hot-button issue as different sports try to balance inclusivity with ensuring fair competition.

International governing bodies in a number of sports, including cycling, swimming and athletics, have tightened policies to effectively ban transgender competitors.

US President Donald Trump signed an executive order in February seeking to ban transgender athletes from participating in women's sports.

Former British swimmer Sharron Davies, who won an Olympic silver medal at the Moscow Games in 1980, has been outspoken over the issue, saying transgender athletes should not compete in women's sport.

"I think it's just really important that we can define what a woman is," Davies said, adding it was time for sports bodies to "protect every female athlete."

"It doesn't mean to say that we can't respect people across the whole of society, however they wish to present themselves," she said.

"My position was always one that, biologically, women are very different from men." (AFP)