When Ruth Anderson, London tax partner at KPMG, became the first woman to be appointed to the board of a Big Five firm in 1998, she was amazed by the considerable press interest.

'It didn't seem to be such a big issue for me. I hadn't really thought about being in a minority before,' she says. 'Although I have to say, I do think about it now.'

Women make up approximately half of KPMG's graduate intake, but only about 11% of the firm's partners. While people will make decisions about careers and families along the way, Anderson maintains that there is something else stopping women from staying on and climbing up the ranks.

'I don't think there's intentional bias against women moving forward and being promoted, but I do think performance measurements tend to be biased towards male behaviour,' she says. 'Certain female talents are maybe not being recognised and so some women are slipping the net.'

This point is perhaps backed up by the fact that nearly 40% of the firm's partner candidates this year were women; contrasting significantly with the actual percentage of female partners.

Anderson adds that people go to where they feel comfortable and where they feel valued, and that it's human nature to feel comfortable when surrounded by similar, like-minded people. And the more senior women get, the lonelier it becomes because the numbers reduce.

'I've never felt that big business is hostile to women, but at times it is wearing being in the minority. It's hard to describe but if you are always the only woman in a meeting or in the boardroom, you'll often see something slightly differently or come at an issue from a different angle from everyone else. And you have to have quite a lot of self-belief to not question your own views and thought processes,' she says.

Networking is also an issue. 'Somehow men can network more informally; in the pub or on the golf course, or through other sports. And some of those aren't as open to women, or women don't want to do the same sorts of things,' Anderson explains.

Anderson is concerned that female graduates and junior managers look further up the firm and see few women there, and therefore decide that it isn't a good place to stay if they really want a career. It's a problem of perception, she says, because in fact there are lots of senior women at KPMG.

These senior women need to be prepared to 'stand up and take profile', she adds, making themselves more visible through interviews and sitting on conference panels, for example, so that the perception becomes more accurate.

And it's not just recruits who are interested in the number of senior women at KPMG. Potential clients ask how many women are on the board too.

Anderson believes the more diverse an organisation, the better the thought processes and output, and clients simply want to get the best.

While firmly against positive discrimination and tokenism, Anderson is keen that good women be encouraged to stay.

The firm is already making certain efforts on this front.

A KPMG women's network has been set up and has attracted a huge take-up across the firm, from all ages and all grades.

Recruitment brochures include statistics on the number of women in the firm.

Business units are challenged if pay review statistics don't look quite right, and panels for promotion to partner will include at least one woman as a matter of policy.

'I'm optimistic that more women are going to make it to senior roles. It is changing,' says Anderson.

'But we can't afford to be complacent.' she adds.