Teachers at a union event have been told that "there is no legal or even scientific definition of 'biological sex'" - despite April's common-sense Supreme Court gender ruling.

More than 150 people had enrolled at an online seminar hosted by the National Education Union's "trans and non-binary network" following the ruling, which made clear that the terms "woman" and "man" under the Equality Act 2010 relate to biological sex.

During the seminar - called "Solidarity in Practice: Building Sustainable and Effective Cisgender Allyship" - a presenter from the LGBT network at the Public and Commercial Services Union made the controversial claim about biological sex having no legal or scientific definition.

The event claimed to attendees that transgender people can use facilities corresponding with their "gender identity" under equality laws.

More than 150 people had enrolled at an online seminar hosted by the NEU's 'trans and non-binary network' following the ruling

A presentation summary said: "The Supreme Court ruling excluded trans voices.

"But thanks to the Equality Act 2010 we can use correct gendered facilities. For now, no law has changed. Anyone enforcing discriminatory policy on trans people is breaking the law."

But the NEU's guidance flies in the face of advice from the Equality and Human Rights Commission issued after the Supreme Court ruling.

The EHRC's guidance states that "trans women (biological men) should not be permitted to use the women's facilities and trans men (biological women) should not be permitted to use the men's facilities, as this will mean that they are no longer single-sex facilities."

Naomi Cunningham, a barrister and chair of campaign group Sex Matters, said the "trans activist network" at the NEU was among bodies "misrepresenting" the law "because they don't like the outcome of the Supreme Court judgment."

Naomi Cunningham said the 'trans activist network' at the NEU was among bodies 'misrepresenting' the law (file photo)

"It is both wrong and dangerously irresponsible to suggest that the exclusion of trans-identifying people from opposite-sex facilities is breaking the law," she blasted.

"Schools have safeguarding responsibilities for the children in their care, and the risks of letting teenagers self-identify into opposite-sex facilities should be obvious."

She called on the NEU to "rein in extremists within its networks and ensure that guidance given at any official event is compliant with the law."

The presentation also included claims about "Genotypic Sex" being "more complex than XX/XY", referring to chromosome combinations that determine biological sex.

The Supreme Court came under fire from 'activist groups' at the NEU for 'excluding trans voices'

Dr Emma Hilton, a developmental biologist at the University of Manchester, said: "It is extremely concerning that a teacher's union, presumably including science teachers, is hosting an event where ridiculous claims that there is no scientific definition of sex are being made."

Dr Hilton continued: "'Male' and 'female' refer to two different types of people with two different patterns of anatomy, and how those different bodies function in reproduction."

An NEU spokeswoman denied the event was an official union meeting, saying the organisation, "has not yet provided advice to its leadership members, or union reps, since the Supreme Court ruling".