https://phys.org/news/2018-05-years-gender-gap.html

The gender pay gap stood at 18.4% in April 2017 according to the Office for National Statistics. The United Kingdom is numbered among nations with one of the widest pay gaps in Europe, with only Estonia, the Czech Republic and Germany recording higher pay gap rates.

To put that in pounds and pence, for every pound that men earn, women make 80 pence and this disparity has moved very little in the last 15 years.