Women working full-time are being swindled out of £5,000 on average every year through shadowy pay practices, the TUC revealed yesterday.

The gender pay gap means women will effectively work until the end of the year for free and lose hundreds of thousands of pounds over a lifetime.

Women employed full-time earn 15 per cent less on average while the gulf reaches 35 per cent for those employed part-time.

TUC general secretary Frances O'Grady said bosses masked the "huge injustice" through complicated pay structures.

Just 100 companies voluntarily publish information about pay disparity between their female and male staff.

And Ms O'Grady said: "Four decades on from the Equal Pay Act, it's clear we need to take a tougher approach so that future generations of women don't suffer the same penalties.

"One simple way would be to force companies to be more transparent about how they pay staff."

Women lose out to men in almost every sector of work but those in health and media, culture and sport suffer the biggest losses.

Female health workers can expect to take home £16,000 less than male colleagues, which is well over half the average annual wage in Britain.

The chasm in culture, media and sport stands at £10,000 a year.

National Union of Journalists general secretary Michelle Stanistreet pledged to challenge bosses on behalf of members who were underpaid.

"That companies continue to get away with old-fashioned sexism and old-fashioned pay discrimination in the workplace is an outrage," she said.

"It's time they woke up to the fact that treating staff fairly is actually good for business."

The TUC called for more senior part-time posts to allow women, who consisently outperform men academically, to juggle work and childcare.

Ms O'Grady added: "It is crazy that employers are missing out on billions of pounds worth of women's talent, skills and experience every year."

Campaigners also warned that Britain's austerity government is forcing women into the private sector, where the pay gap is almost 20 per cent.