“Women are angry – and rightly so,” says Jane*, reflecting on the mood in her office following last week, when her employer, the Telegraph Media Group, revealed a gender pay gap of 35% in favour of men. “The day after we found out, we said to each other: ‘Right we’ve worked 65% of the day now, it should be time to go home’.”

When the news hit her inbox – an internal email broke the news to staff before they found out elsewhere – Jane says she felt sick. And while the revelations didn’t stop female staff from working in the following days, they certainly didn’t hide how they felt about the news. One Telegraph employee, referencing suffragette Emily Davison, wrote on Twitter: “Suddenly have an overwhelming desire to throw myself under a horse.”

Any UK company with more than 250 employees will have to publish its gender pay gap by 4 April, with the likely result that many women around the UK will experience similar frustration. (Find out about your company here.) Jane wasn’t surprised to find out there was a substantial difference between the average hourly earnings of men and women in her workplace – “You only had to look at the gender balance of the senior staff,” – but it’s still different to see the numbers confirmed in black and white. 

The gender pay gap, which measures the difference in average hourly earnings in an organisation, is different from equal pay – ie getting the same money for the same job – which has been a legal requirement for nearly 50 years. The pay gap data also reveals information such as the percentage of women working in the lowest-paid and highest-paid jobs in an organisation.

“These new requirements will send shock-waves through organisations as women realise they feel devalued, diminished and cheated,” says Alison Marshall, spokesperson on equal pay for the Women’s Equality Party. Marshall predicts that it will be a watershed moment for women in work.

Also among the 9,000 companies that released gender pay gap data in recent weeks was Marks & Spencer, where female employees are paid, on average, 12.3% less than male workers. Lisa*, who works in M&S head office, says she had always suspected that was the case: “It’s always been a source of resentment that the men I work with are getting paid more than me. Without exception.”

Despite long suspecting the inequality (and feeling angry about it) Lisa never challenged her salary, because she has felt bound by another issue felt keenly by female employees – childcare. Lisa’s boss sometimes allows her to work flexibly, taking her work home so she can juggle motherhood and a career. “So I never said anything about the money,” she reflects. 

Following the publication of M&S’s gender pay gap, Lisa was told that her salary will be increased quite significantly. But even this rise will still leave her relatively underpaid. She won’t be challenging it further. “I work in a very male dominated industry and I’m grateful for my continued employment,” she says. 

If you want your company to address its gender pay gap – or if you think there’s an issue around equal pay – Sam Smethers, chief executive of the Fawcett Society, says there are a number of things you can do. 

“Talk to your union rep if you are in one, or join one. Raise it with your line manager, talk to your female colleagues as you might find that others may be affected too, or raise it in your women’s network if you have one.”

For women in smaller companies, which do not have to report on their gender pay gap, Smethers suggests starting the conversation about pay yourself: “People can find it uncomfortable to talk about pay, but without transparency we can’t challenge unequal pay. We are calling on women everywhere to take that first step and simply have the conversation about pay with your colleagues.

“At the current rate it would take 200 years for women and men to have the same economic opportunities, so have the conversation, we will not wait that long!” 

Whichever path you choose, it is better to focus on taking a hard line with your employer, rather than colleagues who have benefitted from the disparity. Nic Hammarling, head of diversity at business consultancy Pearn Kandola, says ultimately you have to be prepared to walk away.

“If you genuinely believe that you are being paid less than a colleague for the same work, this is likely to be indicative of further inequality throughout the business. It’s possible that this will go on to be reflected in other areas, such as promotions and bonuses,” says Hammarling. 

Amy* started her new job as a university postdoctoral researcher on the same day as a male colleague, whose two-year contract would mirror hers. She noted he had not yet defended his PhD so was a step behind her on gaining his qualification: nearly 12 months later she discovered he had been getting a bigger pay cheque all along. 

“I thought it was a mistake and they would rectify it as soon as I pointed it out,” she says. “Instead, they just told me I was making a fuss. I came to academia, naively thinking that people were valued for their ideas and not gender.” Like  other women we spoke to, she stayed in her job for a further 12 months before moving somewhere else.  

Deputy head teacher Abby*, who works at a special needs school, recently found out that male deputy heads at other schools are being paid between £10,000 and £20,000 a year more than she is. She raised the issue with her bosses, and even threatened to resign – but her employer has not raised her salary.

“I’ve made the point that if I were to resign my job would be advertised at £10k more than I get. Yet I still get told to shut up about it,” Abby says.

When she joined the school in 2015, Ofsted rated it inadequate; in its most recent report the school inspectorate said it was no longer performing poorly, Abby argues that she is largely responsible for that change. “And there are blokes on £20k more than me [at other schools] who are actively fucking up their schools, getting inadequate as a rating, and doing less of a job role than me in terms of responsibility!”

Also in the public sector, Allana, 58, is one of 60 women in an ongoing equal pay claim against her former employer, HMRC.

“I was paid £5,000 less than my male comparator doing the same job. We were equally experienced and equally competent,” she says. Salaries aren’t just a short-term issue – Allana is affected even now she is retired. “When we were approaching retirement I knew his greater annual salary would be reflected in his pension and thus he would be benefitting from the pay discrepancy for what could be decades.”

The Association of Revenue And Customs Union, which is helping the women with their claim says that HMRC denies any wrongdoing and says it did not discriminate based on gender, but was limited in offering more money because of public sector pay freezes. 

When asked to comment, a spokesperson for the HMRC said: “We are happy that our gender pay gap results sit in line with other civil service departments.”

*Names have been changed on request