Only 13.6% of film directors working in the UK are women, according to a new report.
The study commissioned by the professional association Directors UK showed that the percentage of UK films directed exclusively by women has barely changed in 10 years.
The percentage has risen from 11.3% in 2005 to 11.9% in 2014.
Suffragette director Sarah Gavron, called the figures "shocking and startling".
"Film, of course, influences our culture, which is why it is vital to have diversity and more gender equality both in front of and behind the camera," she said.
"We need to work to shift this imbalance, and it seems the only way to do this is to be radical, rather than waiting for something to change."
The society is calling for half of all publicly-funded films to be directed by women by 2020.
They are calling for films to meet diversity criteria, which would include gender factors, before they receive government funding.
They say their suggestion of a 50:50 split in public funding is something that has been achieved in other countries, such as Sweden.
Beryl Richards, chairwoman of Directors UK, said it was unacceptable that "this level of inequality continues to go unchecked - not least the film industry that plays such an influential role in our economy, our society and our culture".
"With such comprehensive evidence we can now pinpoint and address the areas that need the most attention and focus on rectifying it."
She said part of the blame must be in part a lack of a regulatory system to enforce gender equality.
The report claimed a vicious cycle exists in the industry in which new female talent is discouraged by a lack of role models, which in turn leads to a smaller pool of next generation female directors.
Figures show that while 50.1% of film students and 49.4% of new entrants to the industry are women, just 21.7% of publicly funded films had a female director in 2014 - a figure that has dropped from 32.9% in 2008.
In January a study showed that just 9% of Hollywood's highest grossing films last year were directed by women, the same level as 1998.
Last October, it was reported that the Equal Employment Opportunity Commission in the US had begun contacting female directors to investigate gender discrimination in Hollywood.