The number of women holding senior posts in politics, the law and the media has fallen compared with last year, according to a report.
The Equality and Human Rights Commission (EHRC) said that in 12 of 25 job categories it studied, there were fewer women holding top posts.
Women's representation had increased in eight areas, including company directors and the civil service.
The EHRC said some women faced a "concrete ceiling", not a glass one.
The commission also wants more flexible working to help women rise to the top.
The EHRC said its annual study of women in top positions of power and influence across public and private sectors showed the biggest number of reversals since the report was started five years ago.
Nicola Brewer, the chief executive of the EHRC, said: "Workplaces forged in an era of stay-at-home mums and breadwinner dads are putting too many barriers in the way, resulting in an avoidable loss of talent at the top.
Sun editor Rebekah Wade is one of the few women at the top of her career
"We always speak of a glass ceiling. These figures reveal that in some cases it appears to be made of reinforced concrete."
According to the report, there are now fewer women MPs, cabinet members, national newspaper editors, senior police officers and judges, NHS executives, trade union leaders and heads of professional bodies, compared with 2007.
The number of female media bosses, MEPs, directors of major museums and galleries, chairs of national arts companies and holders of senior ranks in the Armed Forces has remained the same.
Women's representation had increased in the House of Lords and among company directors, council leaders, university vice-chancellors and top civil service managers.
However, in six of these categories the increase was less than 1%.
The commission said opportunities for ambitious women to reach the top of their career were changing at a "snail's pace".
It blamed Britain's business culture of long working days and inflexible working practices for discouraging women who want to both work and raise a family.
Miss Brewer told BBC Radio 4's Today programme: "There is a bit of discrimination still going on and that still needs to be challenged. At the commission's helpline, we still get a high proportion of calls from women at work who are pregnant who are suffering difficulties.
"There are also bigger things going on about how the workplace is organised, how it's really quite inflexible, how there is a lot of occupational segregation and how the definition of success is still quite old fashioned."
The report, Sex and Power, said: "Often women experience a draining combination of outdated working practices and a long hours culture alongside the absence of appropriate high quality, affordable childcare or social care."
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