British theatre has an institutional problem with sexism and gender inequality, according to the authors of a study who say Arts Council England (ACE) is ignoring the issue and failing to help redress the balance.

The research – conducted by the playwright Jennifer Tuckett and the Sphinx Theatre Company – paints a bleak picture of British theatre, with a bigger gender gap in certain areas compared with eight years ago, when the Guardian conducted an in-depth study of the issue.

The research in 2012 – in collaboration with Elizabeth Freestone, then artistic director of Pentabus theatre – revealed that women were vastly underrepresented, with a persistent 2:1 male-to-female ratio in British theatre roles. Tuckett’s latest research has found that in some cases the situation has worsened – for instance, only 31% of artistic directors are women, compared with 36% in the 2012 study.

The authors of the report, which looked at gender representation at all UK theatres that are classified by ACE as a national portfolio organisation (NPO) – say it shows theatre is lagging behind other art forms, after ACE recently released figures revealing 46% of artistic directors across NPO institutions were female.

The study, inspired by the #MeToo and Time’s Up movements, was conducted by Tuckett and a team of researchers who looked at the output of British theatres across their 2018-19 programmes. It also found that of the funding awarded to NPO theatres, 21% was controlled by companies with a female artistic director, and 0.64% of NPO funding from 2015-18 went to women’s theatre companies (defined as those whose aim is to work with women), such as Clean Break.

As two of the best-funded institutions in the UK, the National Theatre and the Royal Shakespeare Company were singled out in the report. The RSC featured no productions by female writers between December 2018 and September 2019, while 25% of the National’s plays were written by women from November 2018 to April 2019.

The 2012 research found 29% of new plays at the RSC were written by women, while 18% of plays at the National were by female playwrights.

Awards were another area of concern, with no new writing prizes awarded to female playwrights in 2018-19 at either the WhatsOnStage awards or the Olivier awards.

The report follows research by Loughborough University that found theatre criticism was another area dominated by men, with 10% of critics being female in 2017. The same study found that only 27% of university professors teaching theatre and drama were women.

Polly Kemp, the actor and founder of gender equality campaign group Era 50:50, said the research supported anecdotal accounts from female actors and directors, who have experienced sexism in UK theatre. “There’s still a sense that you’re taking a risk when you go with a woman,” she said. “The fact that we’re even still talking about it in 2020 should be shocking, but as an actor who is campaigning for increased representation, it doesn’t surprise me.”

The research comes in the same week that ACE published its 10-year strategic plan for the arts, which identified the “persistent and widespread lack of diversity across the creative industries and in publicly funded cultural organisations” as a key issue that needed to be addressed.

Sue Parrish, artistic director of Sphinx Theatre Company, said she was stunned by ACE’s lack of focus on gender in its strategy document. “Despite our efforts and reassurances that representation was being taken seriously, it clearly is not,” she said. “We are not listed in priorities or outcomes at all, there’s no separate reference made to 51% of the population. It’s extraordinary. I’m stunned.”

Asked if British theatre had an institutional problem with gender equality, Parrish said: “There is, and this document underlines it because the ACE seem to not be admitting it and certainly not addressing it.”

ACE said it required all the organisations it invests in to address the issues of inclusivity and relevance, including the position of women in the workforce and as creatives. “Organisations will be expected to set targets on how they will improve the diversity of their organisation and we will hold them to account on the progress they make,” a spokesperson said. “More details on this will be in our delivery plan, published later this year.”

Tuckett said ACE needed to do more to ensure gender equality was being taken seriously at British theatres, and said the 10-year strategy did not offer any “concrete solutions”.

She said women were largely overlooked in the strategy, whereas people from lower socioeconomic backgrounds, deaf or disabled people, and those from black and minority ethnic backgrounds, were highlighted – supporting the study’s finding that ACE seems “focused more on addressing other protected characteristics than gender, whilst all should be addressed”.

Winsome Pinnock, a black British female playwright, said the lack of progress with artistic directors was significant because women in these roles, including Jules Wright – the late founder of the Women’s Playhouse Trust in 1984 – have been instrumental in her progress.

“I’ve been supported all my career, predominantly by women artistic directors,” she said. “I would not have a career if Jules Wright had not supported my work. I’ve got an upcoming new play called Rockets and Blue Lights at the Manchester Royal Exchange which was backed by Sarah Frankcom. They’ve had to fight for themselves and for us.”

• This article was amended on 29 January 2020 to say 25% of the National’s plays were written by women in the period from November 2018 to April, rather than August, 2019.