The data on this are actually quite good, but the media rarely reports it well. The Home Office reports recorded crime together with the British Crime Survey, which is a half-decent measure of crime experienced. A quick flick at the original data (see e.g. http://rds.homeoffice.gov.uk/rds/pdfs10/hosb1210.pdf) suggests that 'the report rate is up' is exactly what's going on here.
'Most serious sexual crime' recorded by the police ws up 7%, but the BCS datashow 'There were no changes in the overall prevalence of sexual assault between 2008/09 and 2009/10. The overall prevalence of sexual assault has fallen since 2004/05'. The simplest and most likely (though not only) explanation of the data is that there are slightly fewer sexual assaults going on but significantly more of them are resulting in a crime being recorded by the police.
It's still a startlingly low rate of reporting, though.
no subject
'Most serious sexual crime' recorded by the police ws up 7%, but the BCS datashow 'There were no changes in the overall prevalence of sexual assault between 2008/09 and 2009/10. The overall prevalence of sexual assault has fallen since 2004/05'. The simplest and most likely (though not only) explanation of the data is that there are slightly fewer sexual assaults going on but significantly more of them are resulting in a crime being recorded by the police.
It's still a startlingly low rate of reporting, though.