The UK Government have been urged to cut funding from community sports event Parkrun if they don't reverse their current policy on allowing biological males to compete in female categories.
A report published by think tank Policy Exchange, noted that at least three Parkrun records in the female events were held by biological men.
When registering for a Parkrun, competitors are allowed to record their self-identified gender as opposed to their sex.
The report, which is backed by British Olympians Daley Thompson and Sharron Davies as well as tennis icon Martina Navratilova, highlights that the policy has led to three instances where transgender women have set record.
Sian Longthorpe gained national attention earlier this year when she smashed the previous record in the 45-49 category at Porthcawl in South Wales by over a minute with a new time of 18.53 minutes.
The report said: "Given the fact that men generally have a performance advantage over women of at least 13 per cent, it is unlikely a biological female will beat Longthorpe's time in the future."
It also pointed to transgender athlete Lauren Jeska, who has held both Aberystwyth's ages 35-39 records.
The report calls for Sports England to introduce a one-size-fits-all policy where the "female category must be restricted to biological females" for all events.
And if any sports refused to change their policies within the next 12 months then the Government were urged to step in and strip them of their funding.
It read: “The Department for Culture Media and Sport (DCMS) must require all national governing bodies, within 12 months, to update their policies to ensure there is a protected female single‑sex category.
"This should be made a condition of funding, with taxpayers’ funding withdrawn from those that do not protect female same‑sex sport.”
Maria Waite, a Parkrun director, wants to see the community event make the changes to avoid "alienating women".
Sian Longthorpe holds the Porthcawl Parkrun record for the 45-49 category
"I feel very disappointed that Parkrun cannot see how their current policy is so unfair to women.
"They accept funding from Sport England, Parkrun results are published every week on the Power of 10 website and yet when challenged the response is that Parkrun is not a sporting event.
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Martina Navratilova has backed the report
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"They can't have it both ways and are alienating women.
"I am aware that there have been discussions over stopping publishing weekly results and statistics as away of avoiding addressing the problem, but this again will disadvantage women."
