Why are so few politicians women?

[MMMarmite]

They still make up less than a quarter of MPs. At first glance it seems hard to understand, given that roughly 50% of voters are women.

Does anyone know what the main factors are? Are voters less likely to vote for a women? Is there discrimination that prevents women becoming candidates? Is it due to unfair treatment in the press? Are women less likely to want to be a politician, and if so why?

Splitting life between home and London, working most weekends at community events, evening surgeries and I guess the general 'old boys' atmosphere that persists in Westminster.

Those are my observations of someone I know well who is an MP.