I am an EU (Dutch) citizen currently resident in the United Kingdom of Great Britain and Northern Ireland. I am currently registered to vote. I will move to Germany soon. According to yourvotematters, I can only unregister to vote in one place in the UK by registering in another place in the UK. There is information on moving "overseas" on the electoral commission website, but that applies to UK citizens. I don't have the right to vote in UK elections after I leave (nor would I want to). I could just depart without unregistering, but the electoral office will think I'll still be living where I am now, and I don't want that voting cards or other material with my name on it get sent to my current address when I no longer live here. How do I permanently unregister to vote? I have no intention to return to live in the the United Kingdom again.
If I were you I would inform my local Electoral Registration Office of my change of address, note that the new address is not in the UK, and ask them to remove me from the electoral register, or, if that is not possible, at least to refrain from sending anything to me at the old address.