Women will not earn the same as men for almost half a century if the current slow pace of closing the gender pay gap continues, campaigners have warned.
New figures showed that the gap for full-time workers has fallen by 0.2% to 9.4%, the lowest since 1997, but little has changed for the past four years.
For full and part-time employees, the pay gap remained unchanged at 19.2% this year compared to 2014, the Office for National Statistics reported.
TUC general secretary Frances O'Grady said: "Progress on closing the full-time gender pay gap has slowed dramatically over the last few years. If it continues to fall at this pace, we're looking at nearly half a century before we have pay parity between women and men.
"Women need a labour market that doesn't discriminate against them. Stronger action is still needed. While bringing in mandatory pay gap reporting is a welcome step, it must not be delayed.
"David Cameron should extend the law to medium-size companies as well as large employers, and companies that don't comply with the law should be fined."
Sam Smethers, chief executive of the Fawcett Society, said: "This is no cause for celebration and proves again why we must speed up the pace of change or future generations of women at work will continue to lose out.
"Employers need to review their pay systems, publish their pay gap figure and develop an action plan.
"Government must invest in our childcare infrastructure and support mums and dads to share caring responsibilities, and we must remove barriers to career progression and career choices."
The gender pay gap remains virtually eliminated for women under 40 and has fallen for all women over 40 in full-time employment, said the Government.
In England, the gender pay gap is the highest in the South East at 22% and lowest in London at 16.3%.
Minister for Women and Equalities Nicky Morgan said: "We have been clear that you can't have true opportunity without equality and that's why eliminating the gender pay gap is a key priority for this Government.
"These figures confirm the need for us to drive forward change. That's why we are working with business to ensure all large employers publish gender pay gap information, including bonuses.
"And most importantly we'll tackle the underlying causes of the gender pay gap. We will ensure that women are given the support they need to progress from the classroom right through to the boardroom."
Prime Minister David Cameron tweeted: "It's great the gender pay gap is at the lowest level since records began. There's much more to do: true opportunity only comes with equality."
The figures showed that median weekly earnings for full-time workers were £528 in April, an increase of £10 or 1.8% on the previous year, following annual growth of 0.2% the previous year.
Adjusted for inflation, weekly earnings rose by 1.9% on last year, the first increase since 2008.
The bottom 10% of full-time workers earned less than £297 a week, while the top 10% were paid more than £1,035.
The average earnings of 16-17 year-olds are still below the level they were before the financial crash.
Weekly pay among the UK's youngest workforce is 10% lower than that in 2007.
Every other age group has seen their salary rise over the same period, with some enjoying an increase of almost 20%.
On average, 16-17 year-olds in full-time jobs earned £161.90 a week in 2015, down from £179.90 in 2007.
By contrast, the weekly wages of 18-21 year-olds have gone up from £265.50 to £302.20, a rise of 14%.
Older workers have enjoyed the biggest jump in pay, with people aged 50 and over seeing their earnings rise by 19% since 2007.
Matthew Whittaker, chief economist at the Resolution Foundation, said: "The long overdue return of real earnings growth is very welcome.
"But the return of rising pay is just the first step on the long journey back to pre-crash wage levels. If last year's pay recovery is sustained it will take another six years to recover the ground lost since the crash. And it will take even longer for workers in their 20s and 30s."
Kate Green, shadow women and equalities minister, said: "Progress on addressing the gender pay gap has been painstakingly slow under this government.
There were 209,000 jobs that paid less than the national minimum wage in April - 0.8% of all jobs, down from 222,000 last year.