Mushroom, you need that certificate that says that you are not crazy (most of the times you only have to pay for it) and then take an exam at the offices of Guardia Civil. i think those exams are taken on a monthly basis. Be careful because even if your friend has a farm, you can be doing something illegal. The property needs to has a hunting ground status, if not, you cannot hunt.
And of course you will also need to pay for the hunting license of catalonia.
I'm afraid that it's a pretty tough work to find out who is the landowner of a certain amount of land in the Uk...