One possibility is to contact Justice for Women. There isn't alot of content on their site itself, but they may have the information or be able to point you in the right direction.
Part of the answer can be gleaned from the January 2012 British Crime Survey Supplementary Report: K (ed.), Osborne, S, Lau, I and Britton, A. (2012) Homicides, Firearm Offences and Intimate Violence 2010/11: Supplementary Volume 2 to Crime in England and Wales 2010/11. London: Home Office.
On page 16, it give this definition - "The term 'homicide' covers the offences of murder, manslaughter and infanticide. Murder and manslaughter are common law offences that have never been defined by statute, although they have been modified by statute."
In 2010/11, 435 homicide victims were male and 201 were female. There were increases in both the number of male victims (up 5% from 413) and the number of female victims (up 3% from 195). (Page 18)
Over half (52%) of female victims aged 16 or over had been killed by their partner, ex-partner or lover (93 offences), This is similar to previous years with the proportion of female victims killed by a partner or ex-partner having fluctuated between 41 and 57 per cent over the last decade (between 80 and 117 homicides per year). In contrast, only five per cent of male victims aged 16 or over were killed by their partner, ex-partner or lover in 2010/11 (21 offences) (page 21)
Now, this report includes tables showing the proportion of males charged with murder or manslaughter that were acquitted and those convicted, and a similar table for women. What isn't in the report, but must be SOMEWHERE is the proportion of men convicted for killing a partner vs the proportion of women convicted for killing a partner. Anyone know how to get extra info out of the Home Office?