he bulk of the answer goes tho - it's probably what you achieve once in the force that matters most, irrespective of what educational qualifications you have. Obviously doing well there won't harm...
You can take pretty much the GCSEs you want when you want to be a psychologist, but you do need to do a double science GCSE (double science psychology), which you probably already ready know, even...
At least 4 GCSEs (grade C or higher), including a C or higher in a science subject (preferably chemistry or biology) or maths, as well as an A-level in either chemistry or biology