Some people here did O levels, so I can only assume GCSEs are equivalent; but then I didn't find a huge jump to A-level so maybe I am wrong.
And to follow your last post - the ATPLs aren't that hard (depending on your background) - and with your background I am sure that you will fly through them with ease.
YOur previous educational background is the kicker here (and why people keep saying it will help you get through). If you strugged/dropped out of GCSE physics you will probably struggle with things like PoF. If you didn't, you probably won't.
(And as I proved in my last post - you obviously don't need to 'know' much to pass an ATPL; just remember it for a few weeks
)