For some years Women in Music (UK) has been doing a survey of the
numbers of women represented in the BBC PROMS season. The Proms is the
largest classical music festival in the world.
You can read this year's survey results here.
NOTE: Anyone is welcome to quote these statistics, but please mention the source. The figures for past Proms seasons are also available on the Women in Music (UK) website: http://www.womeninmusic.org.uk/