London (AFP) - A tranquil pond on London's Hampstead Heath has become the latest battleground over gender identity after a decision to allow transgender people to bathe in the women-only enclosure.

The issue has divided female bathers between those who want to preserve a "sanctuary" and those in favour of "inclusiveness".

The oasis amid the noise of the British capital is one of three fee-paying ponds that have been open for swimming for several decades in the north London park.

Another is for men only, while the third is mixed.

On a scorching day in the middle of a summer heat wave, around a dozen women -- some topless -- read or chatted around the pond, while some cooled off with a dip.

"For many women who come here, you're in your own little world," said Ann Haidari, 51, a teaching assistant who comes to the pond several times a week, all year round.

"I really love my privacy here and I imagine most people who come here want that," she added.

"I love the fact that it's very much a female sanctuary. It's a rare thing."

The decision late last year by the City of London, which governs the green space, to allow men identifying themselves as women to access the pond and its changing rooms has unsettled many regulars.

- 'Uncomfortable' -

"These rules are very open to abuse. Self-identification (as a woman) is quite ridiculous," said Amy Desir, a 30-year-old mother of two who strongly opposes the measure.

"We're in a vulnerable situation. You might be bathing topless. It's about privacy, dignity, and our rights. It's an attack on our safety," she said.

Desir said women with daughters and visitors of different religions such as Orthodox Jews and Muslims who have strict cultural rules were particularly affected.

"It's a very different atmosphere," she said, adding that one day they were joined by a "man who was trying to wear a costume, but obviously he had a penis so it didn't quite fit."

"The space where women felt free and relaxed is now a space where they are feeling uncomfortable," she said.

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Clare Stewart, a 58-year-old acupuncturist, said she comes regularly with her teenage daughter because "I don't want to be bothered by predatory men".

"They could go to the men's pond, there's no need for them to come here," she added. "It would blow the whole thing apart."

But other bathers defended the "inclusive" move, including writer Anna Russell, 53.

"You don't think anybody who's a blokey bloke would have the balls to come here," she joked.

"Maybe make a separate space for their (transgender) privacy," suggested 64-year-old Vicky Joseph.

"That would solve the problem for people who find male genitalia offensive," she said.

- Self-declaration -

Desir believes the City of London is one of many organisations that have adopted similar measures in anticipation of government reforms to the Gender Recognition Act, to make status change "less bureaucratic and intrusive".

Currently, a certificate of sex change can be obtained even without transformative surgery, if the person has lived for at least two years as a member of the desired sex and can provide a medical report diagnosing gender dysphoria -- a condition in which gender identification does not correspond with biological sex.

A self-declaration procedure will be considered in a consultation to be launched in early July.

Opposing the move, Desir launched the #ManFriday campaign this year, with females posing as males accessing men-only places and events highlighting the implications of gender self-identification.

In May, in one of their most publicised stunts, they swam in the men's pond before being removed by police.

"The men started very angry, they were shouting at us, but once they understood why we were there they were actually very supportive," Desir said.

City of London officials refused to confirm who was allowed in the male-only pond, saying only that "all lifeguards and managers at Hampstead Heath ponds have taken transgender awareness training courses".

Under pressure from an online petition signed by more than 12,000 people, the government already appears to be relenting.

Responding to the petition, the government said it "has not yet decided whether or not to introduce a self-declaration model, and will not change the Equality Act 2010 provisions which support organisations to run single-sex services" such as toilets, changing rooms or shelters, it said.