Groundbreaking legislation forcing companies to disclose their gender pay gap for the first time has revealed that almost nine out of 10 public sector organisations pay men more than women.

As government departments, councils, NHS trusts, universities, schools and other public bodies with more than 250 employees scrambled to report their gender pay gap before the midnight deadline on Friday, reported figures revealed that women in the public sector are paid on average 14% less than their male colleagues.

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Despite threats that organisations could face court if they failed to report their gender pay gap, a number of public sector organisations – which employ 16.6% of the UK workforce – were yet to submit their figures at 4pm on 30 March, hours before the deadline.

The figures, compiled as part of a data-gathering exercise unmatched across the globe, have provided unprecedented insight into the pay structures of public bodies, revealing the most gender-balanced workforces, and those with more work to do.

“These figures show us what we expected – we still see an underrepresentation of women at the top and and overrepresentation at the bottom,” said Sam Smethers, chief executive of the Fawcett Society. “The public sector matters for women because it is women who are overwhelmingly dependent on public services, so getting women into decision-making positions is key.”

In the NHS – one of the biggest employers in the world, where 77% of the workforce are women – significant pay gaps have been exposed.

The Queen Victoria Hospital NHS foundation trust in East Grinstead had the dubious honour of having the worst median pay gap, with women paid an average of 59p for every £1 a man is paid. In an accompanying report the trust, which is made up of three-quarters women, said the figure was influenced by its size and the fact that consultants – who were more than twice as likely to be men – made up a higher proportion of its workforce than other trusts. It had not responded to requests for further comment on the gap at the time of writing.

Local government, which employs more than 1.5 million people, 78% of whom are women, has also come under scrutiny.

Quick guide What is the gender pay gap, and what must UK companies report? Show Hide What is the gender pay gap? The gender pay gap is the difference between the average hourly earnings of men and women. The figure is expressed as a proportion of men’s earnings. According to the ONS, the gap between what UK male and female workers earn – based on median hourly earnings for all workers – was 17.9% in April 2018, down from 18.4% in April 2017. Data in 2018 showed that men were paid more than women in 7,795 out of 10,016 companies and public bodies in Britain. What is being published? All companies and some public sector bodies in Great Britain, except Northern Ireland, with more than 250 employees had to report their gender pay gap to the Government Equalities Office for the first time by by 4 April 2018. The second year of gender pay gap reports - and the first indicator of how public bodies and companies are performing - must be filed by April 2019 What’s the difference between the mean and the median figures? Commonly known as the average, the mean is calculated by adding up the wages of all employees and dividing that figure by the number of employees. The mean gender pay gap is the difference between mean male pay and mean female pay. The median gap is the difference between the employee in the middle of the range of male wages and the employee in the middle of the range of female wages. Typically the median is the more representative figure, because the mean can be skewed by a handful of highly paid employees. What will happen if companies don’t report? The Equality and Human Rights Commission (EHRC) said that, while it would approach employers informally at first if they failed to publish figures by the deadline, businesses could ultimately face “unlimited fines and convictions”. However, information published following a freedom of information request by the Guardian showed that no companies have been fined to date despite hundreds failing to accurately file their gender pay gap figures on time.

Of the councils, North Hertfordshire district council had the worst median gender pay gap at 34%. The council – whose workforce is 65% women and 35% men – said 61% of its top roles were taken by men, while women dominated the lowest-paid roles, such as in administration. A spokesperson said: “Many of these jobs are part-time and/or are suitable for flexible working which makes them attractive to women with caring responsibilities.”

To date 318 of the upper tier councils and local authorities had reported their figures with an average median pay gap of 5.4%. All central government departments had also reported their gender pay gap before the Friday deadline with an average median gap of 11.1% – below the national average of 18.4%.

The average gap at the Department for Transport is 23%, making it the only central government department with a median gender pay gap above the national average. This means that for every £1 earned by a man at the department, on average a woman earns 77p. Women are also underrepresented in the top quartile at the department, which is 67% male.

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The department says the gap is explained by a higher number of men in specialist transport roles and that it is making efforts to close the gap. A spokesperson for the department said: “While women are in the majority at the very top of the Department for Transport – including a female permanent secretary and the most senior female job-share partnership in government – these figures clearly show that we still have work to do to reduce the gender pay gap.”

The Office for Nuclear Regulation reported the worst median hourly pay gap among government agencies at 55%. In other words for every £1 a man earns their female counterpart would only earn 45p. The Civil Aviation Authority reported a 42% gender pay gap, followed by the Nuclear Decommissioning Authority at 39%.

Facebook Twitter Pinterest Durham University reported a 29.3% gender pay gap. Photograph: Image Source/Getty Images/Image Source

The figures also revealed every university in the Russell Group in England and Wales pays women less than men based on median hourly pay . Durham University has the largest gender pay gap in the group at 29.3%. Six others reported median pay gaps that are worse than the national average: Newcastle University, University of Liverpool, Cardiff University, University of Warwick, University of Birmingham and the University of Nottingham.

Private companies have until Wednesday 4 April to file their gender pay gap figures, and comparisons between working practices in the public sector are likely to be drawn. More transparent pay structures, increased flexible working, job shares and part-time roles provided more opportunities for women in the public sector, said Smethers.

But she added that recent high-profile pay discrimination cases in local authorities – such as Fife, Birmingham, North Lanarkshire and Glasgow – as well as the new gender pay gap figures exposed persistent sexism. “In 2018 we should not be seeing pay discrimination against women. It’s fundamentally wrong and we have to sort it out.”

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However, although the figures highlight the inequalities between men and women’s standing in the workplace, how much the figures really tell us about the gender pay gap is limited by the figures the government has requested.

All the figures relate to the average pay of full- and part-time employees. In this case where a group employs a large number of part-time workers, positions typically held by women, pay gap may be amplified by a large number of women in part-time work.

Despite the limitations the figures shone a much needed light on gender inequality in the workplace, said Kate Bell, head of economic and social policy at the TUC.

“These figures show us that we have a long way to go before we close the gender pay gap in the public sector – and it is forcing us to ask why,” she said. “We still have pay discrimination, there is still a lack of women in the highest paid jobs, and there is a still a stark difference in how we value work that is traditionally seen as men or women’s work. We knew much of this, but seeing inequality in your own workplace really brings it home.”

Companies scrambled to publish their gender pay gap figures before the 4 April deadline, with more than half of businesses filing this week.

Banks and big technology companies were among those in the last-minute rush, with Unicredit disclosing a median hourly gap of 52%, Google at 16% and Facebook reporting an average difference of 10% in what they pay male and female employees.

A Guardian analysis showed that the average gap of companies reporting has increased, indicating those with a bigger difference in pay have held off reporting their figures. In January the average gap stood at 6.6%, the latest average gap is 10.2%.

A number of other companies filing large gaps are women’s clothing retailer Coast at 40%, FTSE100 company Carnival at 38%, Marie Stopes at 37% and Sunday Times publisher News UK with a 22% gap.

Companies have been threatened with fines from the Equality and Human Rights Commission if they fail to file by the deadline.

Additional reporting by Shivani Kaura and Giacomo Boscaini-Gilroy