The number of women joining the boards of the largest British companies is on the rise, according to a report to be released on Monday. One in four of the FTSE 100 companies has a board on which 25 percent or more of the directors are women, exceeding goals set by the British government, according to the Professional Boards Forum. The organization, which operates in Norway and Britain, helps company chairmen find female candidates for nonexecutive directorships. Six of the FTSE 100 companies have boards on which more than 30 percent of the members are women, the forum found. Another 13 companies have boardrooms where 20 percent of the directors are women. Last year, the British government has implemented a package of measures intended to encourage gender diversity. It included a guideline that by 2015, 25 percent of the board members of the largest British companies should be women. The guideline was one of the recommendations in a report commissioned by the government and written by Mervyn Davies, the former British trade minister, that was published in February 2011. Britain has joined many European countries in stepping up attempts to address the gender gap in business leadership. A decade ago, for example, Norway adopted quotas for women in boardrooms. France and Spain followed suit. According to many studies, mixed-gender business teams perform better than all-male groups, evidence that helped to shift the reluctance in some businesses to hire women executives. Pressure from Brussels has also increased. In March, the European Parliament threatened to introduce quotas for E.U. companies if member states failed to show enough progress in closing the gender gap. Viviane Reding, the commissioner responsible for justice, has campaigned for women to make up 30 percent of European board members by 2015 and 40 percent by 2020. “My guess is that we’ll see more companies with 30, 40 percent women on their boards in the years ahead,” said Elin Hurvenes, founder and chairwoman of the Professional Boards Forum. Women now hold 16.7 percent of the director’s positions in FTSE 100 companies, up from 12.5 percent in February 2011. In recent months, 44 percent of the new appointments have been women. Mr. Davies’s report counted 21 all-men boards for the FTSE 100. There are now eight, which Ms. Hurvenes said represented a “great improvement,” adding, “I’m sure if you give them a year or two, there will be women in these boards.” The pace of change has been slower among the next tier of British businesses, where 98 of the FTSE 250 companies have all-male boards, down from 131 in February 2011. The number of women directors in the FTSE 250 stands at 10.9 percent, compared with 7.8 percent in February 2011. A month ago, Lucy Dimes became the first woman to join the board of Berendsen, a textile services company based in London. Ms. Dimes, a nonexecutive director, said she does not support the hiring of women just for the sake of achieving gender equality. But, she said, there is an untapped pool of female talent in the business world. “There are enough of the right caliber of women to fulfill these roles,” she said. “Probably the most important thing that happened is that women have become more aware that they should make it more obvious they’re looking for those kind of positions.” Roger Carr, chairman of Centrica, a British energy company in the FTSE 100, said he is a strong supporter of gender diversity. His multinational company has already met the government’s goal, with three women on the 12-member board. “Ultimately, it makes the business better,” Mr. Carr said. “That’s the reason you should do it, not because it’s politically correct or indeed encouraged. It’s because boards are healthier, better places for a mixed-gender balance.” Avivah Wittenberg-Cox, chief executive of 20-first, a consulting firm on gender issues and the author of “How Women Mean Business,” said the next challenge is for companies to help the women already on staff develop their executive talents. “Boards have been useful in sort of building awareness about gender unbalance in business, but the real work to me is on executive committees and the inside of companies,” Ms. Wittenberg-Cox said.