There are two sources of data on domestic violence from the British Crime Survey. Estimates of the number of incidents of domestic violence from the face-to-face section of the survey are available from 1981 to 2008-09 and can be found in this table:
http://www.homeoffice.gov.uk/rds/pdfs09/hosb1109tab201.xls
Because of the nature of these offences, more reliable estimates of domestic violence come from the self-completion section of the survey, but these are only available from 2004-05 onwards. We also only report on the prevalence of domestic violence from the self-completion section, not the incidence. Trends in the prevalence of domestic violence from 2004-05 to 2008-09 can be found in Table 3.06 here:
http://www.homeoffice.gov.uk/rds/pdfs10/hosb0110chap3.xls
The issue of making domestic violence a criminal offence was discussed during the Safety and Justice consultation which led to the introduction of the Domestic Violence Crime and Victims Act 2004. The Government believe that the range of existing criminal legislation, coupled with the definition of domestic violence, is sufficient to ensure the maximum discretion in selecting appropriate criminal charges. CPS also flag all domestic violence related crimes.