Nearly half of all directors recruited in the UK's top companies in the past six months were women, helping to improve the gender imbalances at boardroom level by 5% from last year's figures and proves a voluntary approach to improving diversity works, Downing Street says.

A spokesman for Number 10 said that 44% of all FTSE 100 directorship appointments since March were female, and that women now accounted for 17.3% of the boardroom in the biggest companies operating in the UK.

This showed a marked improvement on the 12.5% figure cited in February 2011, when the Women on Boards report was published. At the time, Lord Davies, who authored the report, warned that a failure to improve the gender diversity on boards was damaging business and recommended quotas be imposed for those that failed to reach 25% by 2015.

The Downing Street spokesman added that the possibility of EU-imposed quotas were not necessary when the UK was proving a voluntary approach is successful. However, France, Italy and the Netherlands have imposed the 40% EU quota system.

Board diversity has taken a hit, however, as Reckitt Benckiser (RB) has announced that CFO Liz Doherty is to leave the FMCG listed company, leaving only five female CFOs at FTSE 100 companies.

Doherty, who was appointed in January 2011, will stay until March 2013 and will be replaced by Smith & Nephew's CFO Adrian Hennah.

Rakesh Kapoor, CEO, said: 'Liz and I have agreed that RB's and her way of working are not as well matched as either of us would like, and now is the right time for her to move to a new opportunity.'

While FTSE 100 companies have improved the balance of women in boardrooms, figures in the FTSE 250 remain steadfastly low. According to the 30% Club, women only account for 7.9% of positions at the most senior level and over half (52%) of companies had no female representation outside the FTSE 100.