Yes you can. You will need an E111 or its equivalent (this is changing at the moment and new applications will be issued with a card). You go to your local doctor’s surgery with your passport and a photocopy, your E111 and a photocopy, plus proof that you are a pensioner. You will have to complete a form: BDU solicitud de uso multiple. You will have to say where you live in England, your address in Spain and for how long you will be needing the drugs. It is always a good idea to show the packets of the drugs that you normally take to the doctor and your English prescriptions.
