Three-quarters of musicals staged in the West End over the past decade had no women on their writing teams.
Research by The Stage reveals nearly nine out of 10 musicals had a book written entirely by men, with women credited for the script of just 12% of productions.
The figures represent any time a woman was credited for either the book, music or lyrics of a show, and have been described as “shocking” by industry figures.
A woman was credited for the music or lyrics on just 18% of the musicals counted, despite the inclusion of jukebox musicals such as Beautiful – The Carole King Musical,  or Soul Sister , with music from Tina Turner.
With jukebox musicals removed from the equation, a staggering 91% of musicals had a score written by male composers.
Only four out of the 118 musicals that ran over the 10-year period had a female composer solely responsible for writing the score.
Of these four musicals, just one is by a British composer – Bad Girls the Musical , by Kath Gotts – which played at London’s Garrick Theatre for two months in 2007.
Responding to the research, screenwriter Catherine Johnson, who wrote the book for Mamma Mia!, said she was “gobsmacked”.
“When you think that there are so many women playwrights out there – their voices are heard and they’re writing contemporary, pertinent, compelling drama, so for that not also to be happening in musical theatre, something is really going wrong,” she said.
The analysis looked at all musicals that have run for three weeks or longer in the commercial West End from the beginning of 2007 to the end of 2016. Shows that have run multiple times at different theatres were counted only once.
Women writers were credited on just 16% of all musicals that have run in the West End in the past 10 years
In several of the years counted, a woman was credited for writing either the book, music or lyrics for just one or two new musicals – even when counted jointly with a man. In 2014, not a single new musical credited a woman on the writing team.
Of all the musicals to have run over the past 10 years, only three had all-female writers, compared to 88 shows written by an all-male team.
The three musicals written by women include Bad Girls the Musical, a musical version of Gone With the Wind  with book, music and lyrics by Margaret Martin, and Viva Forever! , which has a book by Jennifer Saunders and music by the Spice Girls.
This contrasts with the number of musicals written by all-male teams, including Joseph and the Amazing Technicolor Dreamcoat, Sunset Boulevard, Matilda the Musical, Sweeney Todd and Miss Saigon.
- 88 – Number of musicals with an all-male writing team
- 3 – Number of musicals with an all-female writing team
- 12 – Percentage of musicals with book credited to a woman
- 4 – Number of scores, out of 118, entirely composed by a woman
- 1 – Number of scores entirely composed by a British woman
The Stage’s associate editor Mark Shenton highlighted a significant gap between the West End and Broadway, which he said had seen a “healthy expansion” of female composers’ works over the past few years, including Tesori’s Caroline, Or Change  and Sara Bareilles’ Waitress.
Shenton said female voices were almost non-existent in the West End, where only two new British musicals were staged last year compared to 13 new American works on Broadway.
He added: “Even the opportunity to get a female voice to collaborate on the women’s story behind The Girls  was passed over in favour of pop star Gary Barlow. So no wonder women are struggling to get their voices heard here; there’s not enough being produced, and when they are, they go to famous white men.”
Bad Girls composer Gotts added: “The problem is that the established stable of go-to talent for any of these big-scale opportunities is still basically an almost exclusively white, male, closed shop.”
Producer Martha Rose Wilson and artistic director Caitlin McLeod from the Coterie, a female-focused new writing company, echoed Gotts and agreed that while men were seen as a “safe pair of hands”, women must “excessively prove themselves” before being given a high-profile platform.
Lyricist Jenifer Toksvig added: “Musical theatre is widely regarded as a very specific commercial art form.
“For as long as we force the genre down such a narrow funnel, those who are well-greased with privilege will be more successful at sliding through than those who are not.”
However, David James, founder and director of training organisation Book Music and Lyrics, which teaches musical theatre writing, argued that if more women wrote “better” work, more would be produced.
He said there was “no doubt” that gender, ethnicity, age and disability were big issues to highlight, but added: “Let’s not forget that there hasn’t been an all-out hit West End musical since Matilda; and if 91% of musicals have been written by men, this means 91% of the flops have been written by men,” he added.
“I would say the answer, for both men and women, is to raise their game and write stronger work. If women write the better work, they will be produced. I don’t believe they will be sidelined because of gender.”
Others including Jennifer Tuckett, director of mentoring programme University Women in the Arts, and Andy Barnes of new musicals producing company Perfect Pitch , called for further investigation into the gender disparity.
Jon Bromwich, executive producer at Youth Music Theatre UK, also highlighted an issue at training level, arguing that the educational system appeared to produce fewer female composers.
He added: “Lack of role models and instruction at a young age are undoubtedly contributory. Ingrained behaviour patterns may mean that young female instrumentalists stay with their instrument while males move into composition.”