Strictly Orthodox women are reportedly preparing to "take action" against the decision to open the Hampstead Heath Ladies Pond to transgender swimmers, which means they cannot, under Jewish law, swim there.

Under halacha, no one can change their gender, and so trans women would not be considered women.

While Jewish law permits Strictly Orthodox Jewish women to be in a state of undress in front of other women, it is forbidden in front of men.

University of Reading Professor Rosa Freedman said on Twitter she had “explained [the concept of] trans to an ultra orthodox chassidic Jewish Rabbi whose wife and her friends will no longer be able to swim at Hampstead Ladies Pond… perhaps the most difficult conversation I have had on the issue to date.”

The rabbi’s wife, Prof Freedman said, “swims there every day…and she wanted to know 'what can we do? and how do we do it?' She is currently creating a group of religious women to take action.”

The change was brought in by the City of London Corporation, which manages Hampstead Heath, after a public consultation.

The corporation claimed the “overwhelming majority” of the 21,000 valid responses to the consultation favoured admitting trans women to the ladies pond.

Opponents of the decision have claimed that close to 50 percent of the responses were deemed invalid, apparently because “they did not address any of the questions on gender identity”.

A JC understands a judicial review challenge is being prepared against the City of London’s decision, in which strictly Orthodox Jewish women are expected to be involved.

Edward Lord, from the City of London Corporation, said: "This policy will ensure our public services do not discriminate against trans people.

"We support a wide range of service users and we want to ensure they can all feel comfortable accessing and enjoying our facilities.

"All communities should be fully respected, and equality and basic human rights upheld."