Having said that, the UK has some pretty clearly defined laws. They're written well, and are easy to understand and are not ambiguous. There are 3 laws relevant here. i) Rape ii) Assault by penetration iii) Sexual Assault. (I'm making the assumption that offences against children are different.)
Rape and Sexual Assault by Penetration are equally serious and are almost identically written, except rape requires the penetration to be done by a penis.
Women can't be rapists under UK law. Women can be perpetrators of the equally serious crime of assault by penetration. Men can be the victims of rape or assault by penetration. Men and women can be the perpetrators or victims of sexual assault.
http://www.legislation.gov.uk/ukpga/2003/42/contents
All crimes of rape and assault by penetration are under reported by victims, and under-recorded by police. It's likely that these crimes with male victims are less reported (more under reported) (and less recorded) than these crimes with female victims.
The UK has 2 sets of crime data. The first is what police claim has been reported. (These are not seen as statistically robust because of variations in what police record). The second is the annual Crime Survey of England and Wales. These are seen as robust statistics.
Here's the reports for "Crime in England and Wales" for year ending March 2015 and year ending December 2015. Note that the sexual offences here also include offences against children. I think that's an unhelpful
http://www.ons.gov.uk/peoplepopulationandcommunity/crimeandj...
http://www.ons.gov.uk/peoplepopulationandcommunity/crimeandj...
The reliance on police recording, and the lack of reporting about sexual offences in CESW means that any stats the UK has for sexual offences are seen by government statisticians as being unreliable.
https://www.statisticsauthority.gov.uk/archive/assessment/as...
From "year ending December 2015":
> Police recorded crime figures showed an increase of 29% in all sexual offences for the year ending December 2015 compared with the previous year (up from 80,265 to 103,614; Table 10a), reaching the highest volume recorded since the introduction of the National Crime Recording Standard (NCRS) in April 2002 and marking the first time that the total number of offences has exceeded 100,000 in a given year. The latest rise remains among the largest year-on-year increases since the introduction of the NCRS, although it is not as steep as those seen in the years ending March, June and September 2015 (36% to 41%).
> Police recorded rape increased by 30% (to 34,741 offences) compared with the previous year, while other sexual offences increased by 29% (to 68,873 offences). Offence categories that directly relate to sexual offences against children[2] contributed 44% to the total increase in sexual offences recorded by the police.
> [2] This includes "Rape of a male/female child under 16", "Rape of a male/female child under 13", "Sexual assault on a male/female child under 13", "Sexual activity involving a child under 13/under 16" and "Abuse of children through sexual exploitation".
The charity rapecrisis leans towards gender neutral language. http://rapecrisis.org.uk/statistics.php
> Approximately 85,000 women and 12,000 men are raped in England and Wales alone every year; that's roughly 11 rapes (of adults alone) every hour
> Nearly half a million adults are sexually assaulted in England and Wales each year
With all these caveats to say that we don't really know the picture around sexual offences in England and Wales I still think it's reasonable to say that sexual offences against adults tend to be committed by men, and that while anyone can be a victim of these crimes (and certainly it's not as overwhelmingly gendered as some people suggest) the victims tend to be female.
But the point being that a woman forcing a man to have sex counts as none of those things. It only ends up in that list if she sticks something in his butt.
Your use of "force" here is unhelpful. We know that juries don't convict because they feel that force is necessary for rape - thus women who don't fight back are not seen by juries to have been forced into sex.
It's much better for us to focus on consent, and to educate people that consent can't involve coercion.
That recognises the under-conviction of rape for women victims; and it also promotes the rights of men to not consent to sex and to have that recognized as the abusive crime that it is.
My aim here - just in case it's not clear - is to make it easier for men to report crimes committed against them, and to make law enforcement record those crimes, and to make juries convict those crimes. I also want to make those things happen for female victims. (And here where I use male / female I don't want to limit to a gender binary).
Obviously a tangent, but this strongly depends on how you define rape. Recent CDC studies find that a huge number of men report being "made to penetrate" women against their will. Most normal people would classify this (sex against your will) as rape, but the CDC only classified it as "sexual assault". Unsurprisingly, if you define men being forced to have sex with women as "not rape", then tautologically almost all rapists are men.
I have the feeling that as society moves towards true gender equality, we'll realise this problem is much less gendered than people currently assume.