The director behind a documentary about the scarcity of working female filmmakers has said the problem is the result of “entrenched” discrimination and working practices.

Earlier this year an annual diversity survey found that just 4% of films made in the US were directed by women, equating to 22 male directors for every woman.

Amy Adrion’s film Half The Picture will screen at the Sundance London film festival, where seven out of 12 films that will be showcased are directed by women.

She told the Press Association: “Habits die hard, this is very entrenched and people have a certain way of working.

“It is a business of relationships and people need to feel comfortable with who they are bringing on to shepherd their big projects out into the world and people are still working on getting comfortable with women in those leadership roles, with women as the artists, with women as the visionary.

“It takes a little bit of mental work to accept that.”

She added: “You can’t underestimate how deeply entrenched these ways of working are, I am optimistic but I have to say I would be surprised if, in a generation, there is a change.”

Half The Picture features contributions from female directors including Girls creator Lena Dunham, Selma director Ava DuVernay, Twilight filmmaker Catherine Hardwicke and 50 Shades Of Grey director Sam Taylor-Johnson.

Adrion said she had been particularly frustrated to see that women who had enjoyed huge box office success, such as Hardwicke and Taylor-Johnson, still faced difficulties.

She said: “Hollywood is a business so people I’m sure will say it’s not Hollywood’s job to give whoever wants a directing gig a directing gig, they are not a charity, but the films directed by women make money and do well.

“And even those women aren’t getting the next opportunity, so that just doesn’t make any business sense and I think that just points to cultural biases we have about women in leadership.

“Once you have Catherine Hardwicke making Twilight or Sam Taylor-Johnson making 50 Shades Of Grey, those women should have big budget movies lined up for the rest of their lives and that hasn’t been the experience for them.

“It’s frustrating because it’s Hollywood leaving money on the table, there is money to be made and they are not choosing that for whatever reason.”

She continued: “It’s a matter of women’s stories always being devalued or considered niche.

“Women are half the world, we are not a minority, we are not niche.

“Our stories are just as valuable as stories centring on men, but that is just a very pervasive understanding of entertainment, that women’s work and stories is not as valuable, and that has been very frustrating.

“If you even look at films coming out of Sundance, incredible films by women directors centring on women, those films still have a hard time in the marketplace. That is frustrating.”

Referring to the rape charges filed against disgraced producer Harvey Weinstein, she said: “The Harvey Weinstein stuff is the tip of the iceberg and it’s more concrete examples of what gender inequality looks like, that I think is the greater problem, is just devaluation of women in the business.”

Sundance Film Festival: London will open on Thursday with the UK premiere of The Tale, starring Laura Dern, and will close on June 3 with the UK premiere of Leave No Trace, starring Ben Foster.