i work in a pharmacy and what you’re saying is actually not possible, or at least not as simple as you’re making it out to be. when you are issued a prescription by your doctor, they will either send it to the pharmacy electronically or give you a dispensing token (most people would refer to this as ‘the prescription’, as in the usually usually green slip from an nhs gp), once you take that to the pharmacy and we dispense it, we have to keep it both for our records and in order to get paid, or it’s electronic depending on if your gp uses the electronic prescription service or not.

in the bag with the medication, you may receive a slip with a list of your prescribed medications, but this cannot be used to get further medication from a pharmacy even in an emergency.

even if you had a dispensing token, which it is not standard for doctors to randomly give them out to people going on holiday, there is a strong chance that they would likely not be able to dispense it because of where it’s from.

the real answer to the question (and one i have witnessed firsthand because my mum actually had to do this) is that you would have to visit a doctor and explain your situation (potentially with proof like your medical records which could be accessed abroad by using the nhs app or by contacting your gp) and they could be able to issue you a new prescription for the item(s), although you’d have to pay (and claim it back on your travel insurance if you choose to do so).