Nearly eight out of 10 companies and public sector bodies pay men more than women as the deadline passed for organisations to report their gender pay gaps.
Businesses with 250 employees or more were required to submit the data on mean and median gender pay gaps to the Government Equalities Office by midnight on Wednesday.
Companies who do not provide their figures after a month's grace face legal action including court orders and fines.
More than 10,000 firms submitted their data, with 78% registering a pay gap in favour of men.
The rest of the employers either have no median gender pay gap (8%) or one in favour of women (14%).
Ryanair is one of the best-known companies in the top 10 of those with the worst gender pay gap, along with the holding company for Millwall FC.
The airline pays women 71.8% less than men on average - when comparing median hourly rates, for every £1 men earn, women earn just 28p.
It says the disparity is because of the number of UK pilots it employs - 546 are male and only eight are female.
Millwall Holdings PLC reported a median gender pay gap of 80%, compared to an average across all companies who have submitted data of 12%.
At the other end of the scale, American Airlines had a gap in favour of women (-3.9%) as did British Telecommunications (-2.3%), while Primark, McDonald's and Costa were among those reporting no wage gap.
Among Premier League football clubs, West Bromwich Albion have the highest median gender gap (34.3%), with Manchester City having the highest in favour of women, paying them 17.2% more than men on average.
The gender pay gap is the difference between the average salaries of men and women and is not the same as equal pay, where firms are required to pay people doing the same job the same salary regardless of gender.