Half of the UK’s working mothers do not get the flexibility they ask for, while those that do work flexibly face discrimination, according to a survey.

The survey of almost 13,000 mothers carried out by the Trades Union Congress (TUC) and the campaign group Mother Pukka found that one in two had had a request for flexible working turned down or only partly accepted by their current employer.

Frances O’Grady, the TUC secretary general, said the survey exposed the failure of the system, with the legal “right to request” flexible working having been in place for two decades.

“The current system is broken. Employers still have free rein to turn down requests for flexible working. And women are too scared to ask for flexible working at job interviews, for fear of being discriminated against,” she said.

The survey found 86% of women working flexibly said they had faced discrimination and disadvantage at work, two in five (42%) said they would fear discrimination if they asked about flexible working in a job interview, and the same percentage said they were worried about their employer’s reaction if they asked for flexible work.

Last month the Department for Business, Energy and Industrial Strategy (Beis) proposed introducing the right to request flexible working from the moment someone starts a job, and obliging companies “to think about what alternatives they could offer“.

Unions said the proposals did not go far enough and that rather than making people ask for flexible working – such as home working, job sharing, agreed predictable hours, term-time working, flexitime and condensed hours – job adverts should set out what sort of options are available for the role.

The TUC – alongside members of the Flex for All alliance including Pregnant then Screwed, Fawcett Society, Mother Pukka, the Young Women’s Trust and the Fatherhood Institute – is calling for employers to publish flexible working options in job adverts, give successful applicants a day-one right to take it up, as well as the right to appeal against any rejections.

O’Grady said: “Ministers need to do more than just tinker with a flawed system. They need to change the law so that all jobs are advertised with flexible options clearly stated, and all workers have the legal right to work flexibly from their first day in a job.”

The survey, which was self-selecting and had 12,855 responses from working mothers, found that 96% of respondents thought the government should give all workers the right to flexible working from day one in a job, and 99% said they would be more likely to apply for a job if it included the specific types of flexible working available in the advert.

“There is overwhelming support for mums and all working parents to be able to work flexibly to manage their work and caring commitments,” said O’Grady. “It’s time to make flexible working the norm as we emerge from the pandemic. It’s the best way to keep women in work and to close the gender pay gap.”

Anna Whitehouse, the founder of Mother Pukka, said she quit her job after she requested to start work 15 minutes earlier so she could pick up her child from nursery, and was denied because her employer didn’t want to “open the floodgates” to others seeking flexibility.

“Flexible working is firmly on Whitehall’s table, but in 2021, 50% of working mums are still having their requests turned down,” she said. “There is a break in the floodgates, but the legal right to flexible working must be made available from the get-go if we’re going to finally change this outdated and discriminative system for good.”