Britain has collapsed from 33rd to 65th place on a global league table of women's representation in less than 15 years, a new report has revealed.
The Counting Women In coalition said in 2001, Britain ranked 33rd globally, slipping to 62nd in 2010 and to 65th this year.
In its Sex And Power 2014: Who Runs Britain? study, it concluded progress in women's representation had stalled or gone backwards - highlighting a 3.5% fall in local government leaders, to 13.1%, in the past decade.
The coalition recommended all political parties take steps to increase the number of women candidates, using positive action if necessary, at all levels of elected office.
And it said the media should ensure coverage of politics includes women and their views.
Report author Nan Sloane, director of the Centre for Women and Democracy, said: "If we really care about who has political power in this country we need to do something about the unrepresentative nature of our elected institutions.
"Along with other excluded groups women have already waited for generations for equal access to power, and we're still being asked to wait decades to achieve it. That's not good enough; we need real change now."
Dr Eva Neitzert, deputy chief executive of the Fawcett Society, said: "Elections are a unique opportunity for parties to make a real improvement in the number of women MPs we have.
"We urge the parties to field more women candidates in safe and retirement seats to ensure women are represented equally in their party."
Katie Ghose, chief executive of the Electoral Reform Society, said: "At the tail-end of this Parliament, we are still not much closer to seeing real gender equality in our politics.
"Despite a headline-grabbing reshuffle earlier this year, the Prime Minister failed to reach his own target of making a third of his ministers female.
"With Britain slipping three places to 65th in the world ranking of parliaments by female representation this year, patience is wearing thin."
Alexandra Runswick, chief executive of Unlock Democracy, said: "It is deeply disappointing that while other countries make progress in improving the representation of women in public life the UK falls even further behind."
Dr Ruth Fox, director of the Hansard Society said: "If the political parties, the government and the media are really serious about tackling this issue then the realistic, practical steps we have outlined could still be implemented in the coming months to improve the culture of politics and the general election campaign."
The Fawcett Society, the Hansard Society, the Electoral Reform Society, the Centre for Women and Democracy and Unlock Democracy joined together in 2011 to form the Counting Women In coalition to address the lack of women in politics.
The group campaigns for the equal presence of women at all levels of elected government in Britain.