Based on the content described in the research document, an appropriate BBFC rating for this film would be:
15
The psychological thriller genre and themes of online relationships, identity, stalking, and mental instability suggest that disturbing scenes and concepts may be depicted. While not as graphic as an 18 rating, a 15 rating indicates that the film may contain strong language, violence, sex, and other mature content unsuitable for those under 15 years old. This rating seems fitting to both challenge younger viewers while still allowing the film to explore its mature themes for an older teenage and adult audience.