Who is more valuable to society – a classroom assistant or a gravedigger? This is not an idle philosophical question, but one being considered by lawyers examining one of 62,000 equal pay claims making their way through the employment tribunals system.

Jackie Gilchrist thinks she has one of the most challenging jobs imaginable, supporting the teaching of children with autism in a mainstream school. Her role requires familiarity with the latest developments in occupational, speech and behavioural therapy, a close knowledge of the national curriculum, extraordinary patience and unwavering kindness. She is paid a salary of about £9,880. Gravediggers employed by the same council, Midlothian, just south of Edinburgh, earn £14,000. Road workers earn more than £19,000.

Union representatives argue that it makes no sense for someone with such a responsible, skilled job helping children with special needs to be paid considerably less than someone who digs holes for a living. About 95% of classroom assistants are women, whereas gravedigging and road maintenance are male careers. Historically, councils have paid male employees far more than their female staff – often grouped together as the three Cs, the cleaners, cooks and carers. Over their career, women can find that they have been underpaid by up to £360,000.

"People think 'That's women's work'. They say 'Oh, you are only communicating with children' and assume that's not particularly demanding. But the communication skills needed to speak to disabled children are very great, and these are much more challenging jobs than just digging a hole in the ground – with the greatest respect to the gravedigger," said Peter Hunter, a legal officer from Unison.

Two years ago, Gilchrist began an equal value pay action against Midlothian council. Her claim rests on making the case that her role is of equal (if not superior) value, not just to gravediggers, but also other "comparators", the road sweepers, the road diggers and the dustmen, some of whom earn almost double her wage. Her legal adviser is confident she can win compensation of about £45,000, but he warns the process of securing compensation is so complex and the claims system so choked up that it may be another eight to 10 years before she sees the money.

Nicola Brewer, chief executive of the Equalities and Human Rights Commission, will this week call on the government to reforms the tribunals system to clear the huge backlog of cases so that women like Gilchrist can get swifter justice.

Employment tribunals are "on their knees" she said, struggling with a 500% rise in claims over the last four years . Most cases so far involve women working for the public sector, the NHS and local government, where pay grades are monitored, but lawyers warn the still-hidden problem in the private sector is even graver. Next year a further 150,000 claims will be lodged, the EHRC predicts, as unions and no-win-no-fee lawyers begin to encourage women to fight for what is owed to them.

But what should have been a triumphant quest for equality has become an impossibly messy scrabble, unleashing hostility between women and their male colleagues, many of whom fear their salaries will be reduced if the women get justice. An undercurrent of gender warfare has emerged.

"We are not a militant group of workers, classroom assistants, and I didn't want to take my employer to tribunal, not at first," says Gilchrist, tired after a difficult day at school. "But the more I looked into it, the more unfair it seemed. The job's not valued. It's seen as a woman's job and it's not valued in any way."

In the past, the gap has been "tied up with social stereotypes about men being breadwinners", says Hunter. Anything perceived to be a caring role, looking after children and old people, has always been rewarded less well than the predominantly male jobs, partly because the skills women bring to the work are regarded as innate, rather than qualities they need to be specifically rewarded for.

Bruce Reid, a gravedigger who roves between the council's 20-odd cemeteries, scraping out seven-foot holes with a mechanical digger, is concerned that his pay could be trimmed if Gilchrist's salary is increased.

He will be arguing that the mental strain of his work, with the constant proximity to death and grieving families, makes it a job that deserves a bigger package. "You can't go home and talk to your wife about what you've been doing all day," he says.

He has joined Gilchrist at the Buccleuch pub in the small town of Dalkeith to talk about the pay dispute and is at pains to be respectful of her work. "Everybody has a level of danger in their job. She has all the children that can flare up. We have cave-ins in the grave," he says, but he is certain his work deserves higher pay. "Nobody wants to be a gravedigger. If a wee bairn is murdered and you have got to bury that bairn, it all goes through your head. It is quite a stressful job."

Road worker Adrian Livingstone, who earns about £19,300 as a gulley operative cleaning roadside drains (another comparator Gilchrist will use in her case), also defends his higher pay packet. "We are out there in rains and blizzards. We are not sitting in a warm building," he says.

There are two key grounds for suing an employer for unequal pay: the relatively straightforward claim that a man who is doing the same job as a woman is being paid more than her, and the second, much more complex equal-pay-for-equal-value case, which involves resolving the nuanced questions under discussion between Gilchrist and Reid.

Part of the problem lies in the bonus systems many councils have which give men in manual jobs an extra 20%-50% on top of their salary. Women in caring roles have never been allocated extra bonus payments. Midlothian council has promised to remove all bonus payments by the end of June.

Across the country, so many cases have been lodged that delays are dragging on into months and years. In one notoriously protracted case, launched in 2002, a significant proportion of the claimants are now dead, but a judgment has yet to be made. Equality campaigners describe the system as a "21st century Jarndyce and Jarndyce". Because the councils have to find the money to pay out enormous compensation packages they prefer to appeal at every stage rather than concede defeat. Last year only 126 cases reached a conclusion in employment tribunals.

Every claim made by each retirement home carer trying to get her salary increased in line with the gardener outside and every school cook suing to be treated as well as the local dustbin man has to be heard individually.

Occasionally, councils have tried to make the women suing for compensation feel guilty for demanding their rights in a way that asbestosis victims, for example, never were. In one now famous case, St Helens council told women that if they continued to pursue their case for equal pay, then school dinners would be at risk and children could go hungry. Gilchrist has received similar threats. "One council member told me we would bankrupt the council," she says.

The delay in settling cases is partly a cost issue. "You wouldn't say it would be cheaper for employers to discriminate against black staff, would you?" says Bronwyn McKenna of Unison.