ONS says full-time pay gap is less than 10% for first time since records began, but overall gap remains almost double that as salaries in general fail to keep pace with inflation

The gender pay gap for full-time workers has fallen below 10% for the first time in 15 years since comparable records began.

The difference between men's and women's median hourly full-time pay fell from 10.5% in 2011 to 9.6% in 2012, according to the annual survey of hours and earnings from the Office for National Statistics.

Women's average hourly earnings grew by 2% to £12 over the 12 months to April, while men's earnings grew by 1.1% to £13.27, prompting one employment expert to claim "women are steadily chipping away at the glass ceiling."

The figures show women now earn an average gross full-time salary of £23,100 – £5,600 less than their male counterparts and £200 less than the gap of £5,800 seen in 2011. But at the current rate of change women's full-time pay will not equal men's until 2040.

Economists said the narrowing gap can in part be explained by men's full-time earnings rising slower than women's. Others suggested a variety of reasons including a cultural shift, more progressive attitudes displayed by bosses, and higher aspirations among women.

While women are better paid than men when it comes to part-time work, the ONS said the fact more women work part-time jobs, which tend to have lower rates of pay, means the overall pay gap remains high at 19.7% compared to 20.2% in 2011.

The TUC said the lack of high quality part-time work is illustrated by the five highest paid occupations – aircraft pilots; chief executives and directors of advertising and PR; marketing and sales; and telecommunications firms – being dominated by men and having "a negligible number" of part-time positions.

In contrast, four of the five worst paid occupations – waiters and waitresses, bar staff, catering assistants and launderers – are dominated by women and have more part-time jobs than full-time ones.

Frances O'Grady, general secretary designate at the TUC, said: "No healthy modern economy should have an enduring gender pay gap and growing in-work poverty. Unfortunately, common sense solutions such as senior level job shares and flexible working are rarely available in the private sector, and are now under attack in the public sector.

"Unless we change the way we work we will never eliminate the pay gap or tackle poverty."

Wages for full-time employees in the UK increased by just half the rate of inflation, the study showed, with the median salary rising by 1.4% to £26,500 in 2012 against inflation of 3% – meaning households are experiencing pay cuts in real terms.

Xenios Thrasyvoulou, founder of the online freelance marketplace PeoplePerHour, said: "Women are steadily chipping away at the glass ceiling. [They] may be starting to win the battle of the sexes, but the workforce as a whole is losing the battle with inflation."

The gap between the highest and lowest paid employees also narrowed, with the hourly earnings (excluding overtime) of full timers in the top 1% of earners falling by 0.2%, compared to a rise of 2.3% for those in the bottom 1%.

The number of people earning below the national minimum wage fell during the past 12 months, the ONS said, from 299,000 in 2011 to 287,000 this year. But the ONS admitted the figures were not exact due to the impossibility of identifying people such as apprentices and trainees exempt from the minimum wage rate or only entitled to lower rates.

Public sector workers earned more than those in the private sector across almost all measures used by the ONS. The median gross weekly pay of full-time employees in the public sector was £565 in 2012, up 1.6% from £556 in 2011, compared to £479 in the private sector, up 1.5% from £472 in 2011.

But the ONS pointed out that many low-paid occupations such as hairdressers, bar and restaurant staff and junior sales roles do not exist in the public sector.