7staroperetta might be able to help with this one! I'm pretty sure you are indeed allowed to do that, as I have heard many people do it. I don't think it has to be Science-based actually, but perhaps it might be what you enjoy most, given your Engineering background. Have you thought about doing a PGDip/PGCert instead? You'd, in essence, be working towards a higher degree, and a good GPA is achievable doing those courses too.
I hear what you're saying. But both the PGDip and PGCert in Science seem to require the BSc degree as a precursor. I think doing a year long diploma or certificate is a great idea. It'll be easier than my Engineering degree, it'll give me the marks I need to get in. I guess I was hoping someone could give me suggestions on a programme to choose as I would ideally like to do something that also happens to teach me the basics and fundamentals of the sciences (chemistry, especially!)