Women are still decades away from attaining the same status as men in public life, research suggests.
Woman hold only 10% of senior posts in large firms, the study says
The Equal Opportunities Commission says the pace of change in politics is very slow, and that it will be 200 years before equality reaches Westminster.
Women now make up nearly half the workforce, but the EOC research says only a minority attain senior positions in both the public and private sectors.
It says action must be taken now to remove the barriers to women's success.
David Conway, of social policy think-tank Civitas, said the findings were "categorically not" down to sex discrimination.
He said the results were due to women preferring to start families.
Mr Conway, the researcher and author of Free-Market Feminism, said: "The fact of the matter is that women are simply making different work-life choices.
"They prefer to be mums or to combine the two work and parenting roles."
In large companies, the judiciary and the police force, only about 10% of senior roles are held by women, the EOC study says.
And while 20% of MPs are women, the rate at which they are progressing in politics is slower than in other areas.
The commission says it will take 200 years for women to gain equal power in politics, unless the main parties make more effort to redress the balance.
Commission chairwoman Jenny Watson said: "Thirty years on from the Sex Discrimination Act, it is time for us to face some stark facts.
"Women will not make it to the top in significant numbers unless action is taken to remove the barriers that stand in their way, and Britain will continue to miss out on women's skills and talents for another generation."
But Iain McMillan, of the Confederation of British Industry, said the EOC were "going overboard".
"It's not realistic to aim for having 50% of men and 50% of women in every workplace because of people's life choices," he said.
"Some leadership roles in senior management require a lot of full-time dedication and simply won't accommodate work-shares or childcare breaks."
Other findings suggested it would take another 20 years before there was equality in the top management of the civil service and 40 years before women were treated equally at director level of FTSE 100 companies.
It would also be another 40 years until there was equality in the senior judiciary.
The research did point out that in some areas women were "reaching critical mass in some areas, including as heads of professional bodies (33%) and national arts organisations (33%)".
The commission has called for a legal requirement on employers to promote sex equality - and for more senior women to be allowed to work flexible hours.