The UK has fallen out of the top 20 most gender-equal countries in the world for the first time after average wages for women in the workplace fell by £2,700 in a year, a new report reveals.

The analysis, by economists at the respected World Economic Forum, found that the UK now lagged behind Nicaragua, Bulgaria and Burundi in the list of those societies where women and men have the most equitable life chances in education, work and health.

Last year the UK was ranked 18th in the Global Gender Gap Report, but this year fell to 26th. The report is unusual in that the index is constructed to rate countries on their gender gaps, independent of their levels of development.

Thus less developed countries can be placed higher up the rankings if they are more equitable – even if their overall earnings, access to education, or health outcomes are lower.

The report found that this year average earning for women in the UK had fallen from £18,000 to £15,400 while earnings for men were unchanged at £24,800.

However, it said there was a small increase in the percentage of women in senior official and managerial positions, up from 34 per cent to 35 per cent, as well as an increase in the percentage of women in tertiary education.

Overall the report ranked Iceland as the most “equal” country in the world, closely followed by Finland, Norway and Sweden. At the other end of the scale, Yemen was the least equal country ahead of Pakistan and Chad.

The UK was ranked 46th for economic participation and opportunity and 32nd for educational attainment.

The authors said that on average across the world in 2014, more than 96 per cent of the gap in health outcomes, 94 per cent of the gap in educational attainment and 60 per cent of the gap in economic participation had been closed since the first gender report was published in 2006.

But they warned: “No country in the world has achieved gender equality.”

“The report continues to highlight the strong correlation between a country’s gender gap and its economic performance,” they wrote.

“Because women account for one-half of a country’s potential talent base, a nation’s competitiveness in the long term depends significantly on whether and how it educates and utilises its women.”

Eva Neitzert, the deputy chief executive of Fawcett Society, said the past five years had seen a number of key markers of gender equality go backwards.

“Any government committed to gender equality must lift the national minimum wage and ensure that any future welfare changes do not disproportionately impact women,” she said. “The Government should lead by example by enforcing the Living Wage in the public sector.”

The shadow minister for women and equalities, Gloria De Piero, said the analysis was a “damning indictment of David Cameron and Nick Clegg’s record for women”.

“Their policies have meant that women’s wages are lower this year than last year and the gender pay gap is back on the rise after years of falling under Labour,” she said.

The top 20 gender-equal states