Interestingly the UK's official statistic authority (which is pretty good and impartial by the way - it's never been afraid to reprimand the government of the time or opposition for misusing it's stats) has just this last week released it's latest research into the gender paygap:
It shows that not only is the gender paygap not an issue on average for women up to the age of 40, but it actually goes in their favour.
It is only past the point where many start to pull ahead because they are less likely to opt to stay at home and sacrifice their career for childcare duties that the paygap moves back in favour of men. Effectively the overall paygap only exists because when people tend to get the highest salaries (when they have the most experience) many women have opted not to pursue that path.
Of course, we should examine why women as disproportionately opting to be the parent that stays at home to perform childcare duties, there's merit in that. But it does seem to imply there's no real bias against women in the workplace, because all things being equal, when children are much less a part of the equation on average, women actually do better salarywise than men in the UK.