The pay gap between men and women who work full time has increased for the first time since 2008, new figures from the Office for National Statistics (ONS) show.
For men, full-time earnings average £556 per week, compared with £459 for women. Since last year, the gap between earnings has increased from 9.5% to 10%.
The median pay gap between full-time and part-time workers is now £4.75 per hour, which could affect women as they are three times more likely to work part-time than men.
TUC general secretary Frances O'Grady said: "Years of a slow, steady progress on closing the gender pay gap has gone into reverse. Ministers should be ashamed of presiding over this latest dismal record on pay.
"It is not right that in Britain today women still earn 15% less per hour than men, a pay gap that costs full-time women over £5,000 a year.
"The light-touch, voluntary approach to tackling gender pay inequality is clearly failing. We need tougher action to force companies to look at their pay gaps, while government can lead the way by making all new jobs available on a part-time or flexible basis."