Mumsnet has reported itself to the UK data regulator after a former employee published the IP addresses of forum users in a dispute over transgender rights.

The parenting site confirmed it had contacted the Information Commissioner’s Office (ICO) and informed the police after the recently departed intern had made a series of posts on Twitter criticising Mumsnet’s stance on trans rights, accompanied by screengrabs apparently taken while she worked at the company that included private information only visible to staff.

In a series of now-deleted posts on Twitter, Emma Healey, who was a paid intern in the site’s press office for six months, claimed that the “vast majority” of discussion of trans issues on Mumsnet “descends into scaremongering and hate speech”.

“Whilst I was at MN [Mumsnet] (Sept 17-Mar 18), there was really no attempt to keep this discussion civil or polite,” she wrote. “Misgendering and deadnaming were completely tolerated, and the internal moderation policy would change pretty much every day.

“There were many staff members, me included, who raised concerns about what was being said on site – but it was never taken on board. Any criticism has been dismissed as a smear attempt by ‘trans activists’ rather than actually thinking about what was being said.”

Healey had had limited access to the personal information of registered users that was not visible to the general public.

IP addresses are assigned to users by internet service providers and can used to ascertain the approximate location of an internet user. Although it is difficult to precisely identify an individual from their IP address without the cooperation of an internet provider, the information can be used to monitor other online activity and to corroborate other identifying information.

Mumsnet has recently been under pressure from trans rights activists over the content on its forums, with some campaigners contacting the site’s advertisers to complain about the tone of discussions on the issue. Justine Roberts, Mumsnet’s founder and chief executive, has publicly criticised the “thought police” attitude to trans rights in the UK and said she believed it was the “right thing to do to allow this discussion to take place” on her site.

A spokesperson for Mumsnet said Healey had now promised to delete all other Mumsnet-related material. The spokesperson said the company believed the former intern had not intended to publish the three IP addresses of forum users and had done so accidentally.

Justine Roberts, Mumsnet’s chief executive, said: “For us this is about civilised debate and free speech. As an organisation we absolutely believe in the rights of transgender people to be safe, happy and supported. However there are parents (including some trans parents) on Mumsnet who also believe that there are some issues - such as the prescription of hormone-altering medication to young children, and the impact of gender self-identification on women-only refuges and other ‘safe’ spaces - that merit discussion.

“We at Mumsnet have always strongly believe that robust, civilised debate is the best way to reach resolution on difficult issues. Some activists disagree with us on the merits of even having of debate and view it as transphobic in its own right.

“Transphobia is against our guidelines and we delete and ban users who are repeat offenders; we’ve also proactively reminded our users of the importance of abiding by our rules, and will continue to do so.”

Healey later issued a statement via Mumsnet apologising for her decision: “I was just mistakenly trying to do what I thought was the right thing as someone with very strong feelings on LGBTQ+ rights – and in doing so, I did something very misguided and frankly awful.

“I have definitely learnt my lesson: not only about not tweeting in anger but about the language I use, being careful what I say, the power of social media and thinking about all the potential outcomes of my actions (not just the outcomes I intend). As such, I am taking some time away from social media and will return with a hopefully more mature attitude.

“I’d like to also apologise to any users who have felt hurt, attacked or vulnerable due to my actions. I recognise that we do not agree on this issue, but I know the impact that my actions may have had on them and their mental health.”

An ICO spokesperson said: “We are aware of a possible incident involving Mumsnet and will be looking into the details.”