Millions of British women will this week know for certain what they have long suspected – that they are working in organisations where men are on average paid much more than them.

The deadline for reporting the gender pay gap arrives at midnight on 4 April. Any woman working in an organisation with more than 250 employees can enter their company name into the government’s website to see the difference in pay between men and women, and find out what proportion of the highest-paid staff members are women. It doesn’t matter if you work in a high street fashion chain (eg Coast, where the median hourly pay rate for women is 40% lower than for men), for a train company (bonuses paid to women at West Coast Trains are 64% smaller than those paid to men) or at Goldman Sachs (where women’s bonuses are 67% lower than men’s) – you’re almost certainly getting less money. At JP Morgan, only 9% of the best-paid employees are women.

What should you do if you are a woman working at one of the worst-performing companies? Is this the week to ask for a pay rise? Should you go on strike? Or are there smarter ways to deal with the fury that these figures will likely unleash?

How terrible is your company? Look at the data

Most organisations are just very bad; some are shockingly bad. Study the data to search for warning signs. Are there more women than men in lower-grade jobs? Does that proportion flip as you go up the pay-scale so that there more men than women in high-paid roles? What is the bonus gap like?

The gender pay gap in trade-union-organised workplaces is smaller than in those where there is no union Unite's Diana Holland

Remember, this isn’t about equal pay for equal work – a large gender pay gap doesn’t necessarily mean your bosses are breaking the law and a small gap doesn’t mean there isn’t pay discrimination. The government’s pay gap website shows what the average difference in earnings is across each organisation. Particularly telling is the section where companies reveal what percentage of the best- and worst-paid members of staff are women – this should give a clear insight into how committed the organisation is towards promoting women.

“Bonuses and performance-related pay are red flags – in firms where it is predominantly men in the senior management roles, big bonuses traditionally go to men,” says Scarlet Harris, women’s policy officer at the TUC. “Men are deciding who gets the bonus and they decide what achievement and good performance looks like in a company; an old boy network can guide those decisions, as well as prejudices about who is the right person to award the bonus to. This could also be influenced by presenteeism; if a woman has caring issues they might be brilliant at their job but leaving to pick up children.”

Join a union

“This is the first thing women who work in firms with a large pay gap should do,” says Diana Holland, assistant general secretary at Unite. “The gender pay gap in trade-union-organised workplaces is smaller than in those where there is no union.” Join a union whether or not your employer recognises one, she advises. “Unions can still support and advise you.”

Unions can support and advise you. Illustration: Ana Seixas

If there’s no union, get together with other women and document concerns about pay. Make a plan for the best way to raise this with the most senior people in the company. “These are really difficult conversations, which you might not want to have individually,” says Holland. “Realistically, most women in the lowest pay grades aren’t going to be able to knock on the door of the head of human resources or the CEO and say: ‘You’ve got a problem with your pay gap, what are you going to do about it?’ Strength in numbers is a good way to go,” Harris says.

Make your bosses feel the heat

Senior people in the organisation may be feeling embarrassed about the numbers. Let them know you’re angry. Make sure they are committed to reducing the gap. If they are feeling ashamed, now is a really good time to ask about flexible work, part-time roles and jobshares.

Ask your company if it has done a job evaluation scheme, and is it more than five years old, Holland suggests. Ask if men and women have equal access to bonuses, overtime, pensions and other payments. Are part-time workers paid fairly when compared on an hourly basis? Has an equal pay audit been carried out? These can reveal whether there are different pay rates for men and women doing the same job, and if women joining the workplace automatically do so on lower rates than men. “Conducting an equal pay audit will assist your employer in ensuring they are not in breach of the law. If they refuse, employment tribunals have the power to order them to do so,” says Holland.

Has your company promised to do better? Interrogate their plans

Many organisations have published action plans setting out how they will tackle the gap. Does it feel like a genuine mea culpa, with constructive proposals for change? If they haven’t published one, feel very worried. “Have they sent out an all-staff email explaining there’s a problem and what they’re planning to do? They should do that, and if they haven’t, that’s a sign that they’re not taking this seriously; that they’re trying to hide it. They need to have come up with an action plan,” says Otegha Uwagba, author of the career guide Little Black Book: A Toolkit for Working Women.

You need to study the explanation and decide if it’s convincing, or a bit cursory and defensive. Is the timeline for improvement helpful or are they promising to get to 50:50 by 2050, when you’ll be retired or dead?

Men should be able take time off without being shamed by a macho culture of presenteeism. Illustration: Ana Seixas

What are they proposing to do about balance at senior levels? Have they looked beyond gender to think more broadly about diversity? “If a company is recruiting diversity to their board after a pay gap fail, then you have more chance of change than if you have a bunch of old white men chanting: ‘We just want the right person for the job.’ In other words: we want to keep hiring people who look and sound like us,” says Sophie Walker, leader of the Women’s Equality party.

Look out for corporate hogwash

The law firm Slaughter and May begins its diversity statement piously declaring: “The principles of equal opportunity and diversity are fundamental to our continuing success.” But the company goes on to blame its 38.5% pay gap on its low-paid female secretaries, and in its glossy internal briefing note decides to recalculate the gap once the “all-female secretarial population” is removed. “We endeavour to treat everyone with attention, courtesy, respect and consideration,” it says. Its all-female secretarial population may disagree.

So many companies reporting a huge pay gap reach for the same lines of explanation: “We just have more well-paid men at senior levels”, they say. They also add: “This is not illegal.” If that’s the end of their explanation, that’s very problematic.

A good sign of how seriously a company takes equality in the workplace is how seriously it takes childcare policies The Women’s Equality party's Sophie Walker

“Are they saying: ‘There are too few women in senior management’? If so, well, d’oh! That’s the problem they have to solve,” says Ann Francke, chief executive of the Chartered Management Institute. “Are they also blaming society and saying: ‘We’re in a sector that doesn’t attract women’? That should be cause for alarm. They need to redouble their efforts.”

Walker adds: “If your company has announced a pay gap and then said, like Phase Eight did, that it’s simply because men want to work in headquarters and women want to work in the retail outlets, then you’ve got a serious problem because your employers can’t or don’t want to understand that women are often forced into shaping their working hours around their care responsibilities.”

Encourage male colleagues to go part-time

None of this will be solved until fathers start taking on more parenting responsibilities. Oxfam, where women are paid 12.5% less than men, realises this, and in its action plan, says: “We are introducing enhanced, shared parental pay for partners, aimed at encouraging more men to take time out for childcaring responsibilities.”

“A good sign of how seriously a company takes equality in the workplace is how seriously it takes childcare policies – particularly paternity leave, so that men can take time off without being shamed by a macho culture of presenteeism – as well as flexible working and leave for carers of elderly and disabled relatives,” says Walker.

Ask for a promotion

Across the board, the gender pay data shows that women are overrepresented in the lower pay quartiles and underrepresented in the top pay band. Because unequal pay is illegal, it’s quite possible you are being paid the same as the men on your level, but haven’t been promoted enough.

If you work at a company such as Coast – which describes itself as a “brand which designs clothes for women who want to look beautiful, feel amazing and stand out” – where there are 867 women and just 12 men, you might be less amazed and more annoyed that men’s bonuses are 50% higher than women’s and their salaries 40% higher. The company says this is because there are more men in head office and recalculates the gap removing head office – but it still pays women 30% less than men (a disparity it perplexingly describes as “far healthier”).

“If I were working in a shop and I knew that the men in head office were getting paid a lot more, I would be asking my bosses how I could progress to working in the head office and what job evaluation has been done to confirm that jobs in head office are more valuable,” Harris says.

Ask for a pay rise – but be clever about it

“You could just go in and say: ‘I’m massively underpaid. Fix it!’ It just may not be the most effective way to do it,” Francke says. Instead, she suggests spending time creating a detailed achievement log, chronicling your recent successes. If a request for a rise is turned down, she says: “You need to ask: ‘What do I need to do to get promoted in the next six months?’ Or say: ‘I want to plot with you how to achieve partnership.’ My view is that being firm and constructive is better than being belligerent. But you have to be firm or you risk being fobbed off.”

Gather as much comparative data as possible before asking – see if colleagues will share details, or give you a ballpark idea of what they are paid; find out what other organisations are paying people of your level. Sam Smethers, chief executive of the Fawcett Society, says: “The only way to know if you are being paid fairly is to ask for specific pay information to be shared – or to act yourselves and share your own pay data. Once you know about any comparisons then you can be in a position to ask for a pay rise. We just have to talk about pay.”

Some research suggests that women do regularly ask for pay rises, but don’t get them as often as men do. “There are double standards about assertive women not being looked on as favourably as assertive men. You have to put that to one side and realise, yes, not everyone is going to like you for asking for more money … but, if the pay rise is important to you, you have to grit your teeth and do it,” says Uwagba.

• This article was amended on 3 April 2018 to remove a reference to the car manufacturer Tesla, as an earlier version used figures from Tesla Engineering Ltd. The electronic car firm had not submitted the company’s pay gap figures at the time of publication.

