I may fly back to the UK to get a top up
Be careful what you say/do as the UK free NHS consultation and NHS prescription price is dependant on your being UK resident. You said you've been in Poznan for a while ... are you still registered with a doctor in the UK and do you still have a UK address (if your NHS doctor knows you live outside the UK, he/she is duty-bound to get you removed from the system).
If you're staying in Poland, as stated you may already be in the system (PESEL/ZUS) in which case registering here is a formality, albeit one you will most likely require Polish to complete, then you follow the ZUS route to any refund of prescription costs or pay a reduced price for your meds. FWIW, I have a GP who speaks decent English, but a cardiologist and a dentist who do not - luckily I moved to Poland with my Polish partner!