Britain's sex equality laws need to be modernised to continue the work done to tackle discrimination, the Equal Opportunities Commission has said.
More women are becoming managers
It is 30 years since legislation first came into force to deal with unfair treatment of women in the workplace.
But the EOC says women are still sacked for being pregnant, and there is still a large pay gap between the sexes.
Chairwoman Jenny Watson praised progress in the public sector, but called on private industry to do more.
Conservative leader David Cameron added: "It is totally unacceptable in a modern, civilised society for there to be a pay gap between men and women doing equivalent work.
"We need to make more of women's talents and skills and prevent them from being channelled into low paid, part-time work below their potential.
"It is morally wrong, quite apart from the practical problems it creates. There has been far too much complacency over this issue: the battle for equal pay still has to be won."
Figures suggest 30,000 women are sacked from jobs each year for being pregnant, and that the part-time pay gap is stuck at around 38%.
Ms Watson said the private sector needed to take responsibility for making improvements by promoting equality and eliminating sex discrimination.
But the commission is warning that without change to the law there will be difficulties for the next generation of female workers.
Ms Watson said: "For many women, sex equality is a thin veneer which vanishes as soon as they take on caring responsibilities.
"Women working part-time earn nearly 40% less than full-time men, a pay penalty that has hardly changed in 30 years."
But the EOC statistics do show changes.
- In 1975, women represented one third of higher education students. In 2005, girls are outperforming boys at school and represent of 56% of those in higher education.
- The number of women in the workforce has increased by a third since 1975.
- In 1975, less than 2% of managers were women. In 2005 one third of managers are women.
- The average household income has increased by around £200 since the mid 1970s.
- New fathers today spend nearly two hours a day on child-related activity, compared with 15 minutes 30 years ago.