The new figure compares with 8.6 per cent last year – the lowest since records began in 1997, when it stood at 17.4 per cent.
The difference in pay of all men and women workers, including those in part-time jobs, has fallen from 17.8 per cent in 2018 to 17.3 per cent in 2019, the report said.
ONS statistician Roger Smith said the gender pay gap increase was not “statistically significant”, adding it is “too early to say” if it marks a change in trend.
He said: “We also saw an increase in 2013 followed by a return to downward trend in subsequent years. However, the downward trend is a slow one regardless.”
For people under 40 years of age, the pay gap for full-time employees is now “close to zero”, the ONS said.
However, the pay gap among 40 to 49-year-olds is 11.4 per cent and more than 15 per cent for those aged 50 to 59 and above 60 – a figure which has not declined “strongly over time”, the report said.
ONS said the difference is due to women over the age 40 being “more likely” to work in lower-paid jobs and are less likely to work as managers, compared to younger women.
Weekly earnings for women peaked for those aged 40 to 49 in 2019 for the first time, the report said.
Full-time weekly earnings were the highest in the City of London at £1,052 and lowest in Newark and Sherwood, Nottinghamshire, at £431.
The number of full-time employees who experienced a real-term pay decrease fell from 43.3 per cent in 2018 to 35.7 per cent in 2019, the report said.
It comes as companies have been put under pressure in recent years to reveal the difference in pay between male and female employees in their ranks.
In 2015, then Prime Minister David Cameron pushed through a policy where organisations with more than 250 employees would have to publish the gap in hourly pay between men and woman each year.
At the time, firms like Ryanair and Jefferies investment bank admitted that they paid women less than half what they paid men.
In the last few years, the BBC has also faced several controversies over equal pay, most notably when China editor Carrie Gracie quit her post saying she discovered the BBC’s two male international editors earned “at least 50 per cent more” than their two female counterparts.
Speaking about the latest figures, TUC general secretary Frances O’Grady said it would take “decades” to close the gender pay gap at the current rate.
She said: “Government must pick up the pace. It’s clear that publishing gender pay gaps isn’t enough on its own.
“Companies must also be legally required to explain how they’ll close them.”