Proportion of music market made up by youth in UK?

how much of the music bought in the uk is bought by youth? does anyone know a statistic for any age categories like 16-18 years old? i need this for a research essay so i need to be able to cite a credible source, much as i'd love to i can't put 'i got this from someone on yahoo answers', and need to be able to put down say the British Phonographic Industry or something similarly high brow, so any links would also be brilliant. that said thanks in advance fore any answers.anything will be a great help