It also worsens with age, with the gap at 20% for women aged 36-45 amd 35% for those aged 46-60.
Heather Jackson, founder of An Inspirational Journey, an organisation that focuses on achieving equal gender representation in business, said the figures show women have to be confident in negotiating a salary that reflects what they are worth.
"This is a wake-up call for women to get paid what they believe they are worth and it’s a wake-up call to organisations too, if they want the best talented women to work for them, they will need to pay accordingly," she said.
"This isn’t a moral issue, this is a business issue," she added.