OK, great. For university entrance you have two things to consider then: the entry requirements in terms of
subjects, and the entry requirements in terms of
qualifications.
For Psychology they'll either not care what the subjects are, or they'll specify that you should have Mathematics or a Science-related A level - and they always (as far as I've seen) include Psychology in the list of subjects they consider science subjects. So you're fine.
Occasionally, you'll come across those which specify
two science subjects, but you can just ignore those unis.
Before we move onto the BTEC, two things to consider:
1. You say that you "don’t see myself going into anything science related". Psychology
is a science.
At university there will be maths involved (for statistical analysis of research data). There will be biology involved (because the brain and our hormones have a significant impact on our behaviour).
2. If you want to be an Educational Psychologist you will need to take a postgraduate degree after your Psychology degree. That postgraduate degree will be a doctorate. (The job title "Educational Psychologist" is legally protected. You need to be registered with the Health & Care Professions Council to use it. They get to decide the qualification necessary for registration. To register as an Educational Psychologist you will need to take a Doctorate in Educational Psychology - DEdPsy.)
The BTEC in Criminology will generally make it harder to work out whether you meet the entry requirements or not. For example, at University of Bath (which I just picked at random) you need to scroll quite far down their Entry Requirements (
here) before you come across a statement which says, "We accept Level 3 Diplomas and Extended Certificates alongside A levels or in combination with each other. You will need qualifications equal to at least three A levels to be considered." They then link you to a page which points our that you'd need two A levels plus a BTEC Extended Certificate. Bath is one of the unis which don't have any subject requirements, so Criminology would be fine.
Let's pick another university at random. University of Wolverhampton. They want 96 UCAS points (A levels, BTECs, or a mix) with no specific subjects required. How about Keel University? They're happy with "Distinction in
any BTEC National Extended Certificate / Subsidiary Diploma and BC in two A Levels, or Merit in
any BTEC National Extended Certificate / Subsidiary Diploma and AB in two A Levels". So again, Criminology will be fine.
Don't get me wrong - an A level in Biology will make this easier (as some of the better university will express a preference for it), and be more flexible if you change your mind later. But if you're not going to get a good grade in it, and you would in the Criminology BTEC, then do the Criminology BTEC.