I must say I'm not well read on criminology as a degree but I know a fair bit about psychology and the world of forensics.
Forensic psychology as a career will most certainly require a BPS accredited degree and the bog standard psychology BSc really is the best way to go for any psychology related career as it is universally accepted and understood.
I've worked in prison psych wards and secure mental health hospitals for forensic patients and if you want to work with forensic patients then you really need to be a psychologist, psychiatrist, mental health nurse, OT or a social worker. I'm not sure how a criminology degree would directly allow you to be able to work with forensic patients.
I would imagine (no expert in this) that a criminology degree would better suit a career in the police force, whereby you wouldn't necessary be working with forensic patients just the general people in the criminal justice system.
I guess the question is, are you interested in criminal justice in general and would like a police based career? or are you interested in the criminally insane and patients who become mentally unwell in jail and those who commit crimes because they become mentally unwell?
The only caveat is that if you are interested in forensic psychology, be warned that it is immensely competitive and will take a decade of post graduate training.
If you just want to do a degree so you can apply for generic graduate schemes/jobs then just do whichever you enjoy most and that may well be criminology with psychology; the BPS accreditation only matters for psych based careers and won't devalue your degree in the wider marketplace.