A police force has been threatened with legal action after telling women to share toilets and changing rooms with trans officers.

Gwent Police has been accused of breaching new equality guidance by saying 'trans members of staff are entitled to use the facilities of the gender in which they present'.

Now a women's rights organisation is preparing to take the force to court, after the equalities watchdog's recommendations were presented to Parliament last week.

The Equality and Human Rights Commission's (EHRC) updated code of practice – which is yet to be approved by MPs and peers – makes it clear that single-sex spaces such as changing rooms and toilets must be used on the basis of biological sex. Transgender people should be offered a gender-neutral space instead of female toilets.

It follows a landmark Supreme Court ruling last year that the definition of a woman under the Equality Act should be based on biological sex.

The Women's Rights Network requested gender policies under the Freedom of Information Act from all forces to see if they were complying with the Supreme Court judgment.

It revealed many are currently in the process of changing their policies, but Gwent Police insisted: 'Trans members of staff are entitled to use the facilities of the gender in which they present. This will be the case from the first day that they present in that gender. It is not acceptable to insist that a member of staff transitioning at work should use separate facilities.'

Under the force's Transitioning in the Workplace policy, toilets, changing rooms and showers for both officers and members of the public are not segregated on the basis of biological sex.

But the Women's Rights Network believes the Welsh force is ignoring EHRC guidance and flouting Workplace Regulations 1992 which make specific provision for separate facilities for men and women, for the purpose of sanitary conveniences, washing facilities, and the changing of clothes 'for reasons of propriety'.

Ceri Rosser, deputy lead for Wales Women's Rights Network, said: 'We have given Gwent Police ample opportunity to address its unlawful policies on single-sex facilities for staff. Our request for a meeting was dismissed out of hand. This cavalier disregard for the law by a Welsh police force serving over half a million people is both astonishing and deeply concerning.

'When the police themselves appear willing to flout the law, public confidence in law enforcement is inevitably and understandably undermined.'

Cathy Larkman, a director at Women's Rights Network and a retired police officer, said: 'It is frankly astonishing that police forces pretend not to understand the consequences for allowing men access into women's facilities.'

Solicitor Ciaran O'Hare, representing the women's group, has written to the force saying: 'If we do not receive a satisfactory response within 14 days, our client reserves the right to issue court proceedings without further notice.'

A Gwent Police spokesman said: 'We are committed to an inclusive workplace where everyone feels safe, respected and able to be themselves.

'Our Trans Inclusion Policy is being reviewed in light of recent EHRC guidance on public spaces, and we await further guidance on workplaces.

'A revised policy will be issued once the latest guidance and legal developments have been considered, following consultation with our staff networks.'