BBFC ratings are just advised ratings, there is no legal law about them. Its the ESRB rating that will determine its proper rating.
BBFC ratings are used for games with certain themes or content in the UK and are legally binding, meaning it is illegal to supply them to people under a certain age (15, 18 etc). Almost every game I own has been rated by the BBFC, with the exceptions being the ones that do not require a BBFC rating and use the strictly advisory PEGI system. An example of such is FIFA, which has no 'objectional' content.
I think it will be rated M in the US, though. We're not as uptight about violence/nudity/language as the Americans are.