We all know the gender pay gap isn't closing fast enough and new research has found that even when women do edge their way into the top 1% of earners, they remain in the minority.The gender pay gap widens among the UK's super rich, with women making up fewer than one in five of the highest earners, according to research published by the London School of Economics' (LSE) International Inequalities Institute.The proportion of women among the wealthiest 10% and 1% of people has risen since the 1990s, but there is a glass ceiling holding them back from joining the top 0.1% of earners, the research found.Just 28% of the top 10% of earners in the UK (on £40,400 or more before tax) were women in 2013. Even fewer (18%) of the top 1% of earners (on £119,000 or more) were women and fewer still were women (9%) among the top 0.1% of earners (those on £456,000 or more).The number of women in the top 0.1% – the wealthiest 53,000 people in the UK – has barely changed in the last two decades.Researchers also found a similar scenario in the seven other countries they studied: Australia, Canada, Denmark, Italy, New Zealand, Norway and Spain, where women made up less than a third of those in the top 10% of earners.Higher up the income ladder, there were even fewer women in these countries, too. They constituted between 14% and 22% of the of the top 1% of earners.The researchers analysed tax data and took into account income from work and other sources, such as investments. They said the results may even be skewed because husbands may have transferred some of their wealth to their wives to avoid tax.There is also a chance that "positive assortative mating" is going on in the marriage market, the researchers said, meaning "women at the top marry men with similar characteristics and are in a position to share assets and their return".Professor John Hills, co-director of the LSE's International Inequalities Institute, said "it is still a male world" right at the top, reported the BBC "Women have managed to increase their representation in the top 10% because of their success in the professions and business, but few of them are among the very wealthiest."One important factor is the way we earn our incomes these days. Alessandra Casarico, associate professor of Public Economics at Bocconi University in Italy, who co-authored the report, told the BBC: "In the old days, the rich were those with property; they have been replaced by CEOs and entrepreneurs, among whom women are not well represented."Women are also prevented from joining the elite clique of top earners by "structural and cultural barriers", said Sam Smethers, chief executive of women's rights charity the Fawcett Society."Unconscious bias, with men recruiting in their own image from informal networks, a male-dominated, long-hours culture and the unequal impact of caring roles, all contribute to perpetuating a no-go area for women at the top. It has to change," she added.