Thanks Cynic - for un-banning the wrongly banned, to Concertina for the sensible and reasonable words, and to LeonSpy for the encouragement. Just in case my experience is of interest to others I am including my response to Phil in Piraeus. I am sure that others will have had similar experiences:
Hmmm - bloody Brexit!!!!
You ask awkward questions and I can only tell you of my experience in regard to them.
Who I arrived here permanently I thought it best to leave all my tax dealings in the UK. I therefor got myself an AFM, but did not register for TAXIS. When Brexit was about to happen I had a chat with my friendly accountant about whether I should pay tax in Greece - which is a prerequisite of getting Greek citizenship. He told me that whilst UK and Greece had a joint tax arrangement this was not the whole story. Greece would assess the tax I should pay on my UK income and would deduct from that total the amount that I had already paid in UK. I reckon this would cost me at least €2000 a year plus 7 years of penalties for not registering for tax in Greece! I therefore continue to be taxed only in the UK and gave up the idea of Greek citizenship.
About 6 years ago I trotted along to the 'Aliens Bureaux' (Police station that deals with immigration) and got myself a temporary resident permit (the old buff coloured one). As this had run out towards the end of last year I went to a lovely lawyer here in Thessaloniki and asked her to find out about permanent resident's permits. You are probably right about these not being a legal requirement BUT I have been to the UK (twice) and Germany (Ugh) in the last 4 months and each time I have been asked if I have a residents permit for Greece - and I produced it. I am not sure what would have happened if I had not got one.
To get a permit from your friendly police immigration department you need:
1. 4 passport type photos of yourself (be careful not to touch them as they reject finger marks).
2. Medical insurance - I found a wonderful agency who provided me with a Lloyds backed insurance for €350 for the year! They are called CROMAR
3. Proof of capital. They will accept (reluctantly) proof of capital in a UK bank or Building Society. I think they want €4,000. If you have a problem try borrowing from a friend for a week - they only need to see that much in your bank on one occasion.
4. Proof of residence for 5 years - i.e. a rental agreement or whatever. They like utility bills. This was all difficult for me as I live with my (Greek) partner in her house and all the utility bills are in her name. Eventually we went and swore a statutory declaration that I had lived with her for 5 years.
5. Your passport. Difficult for you from what you say, but I think essential. I suppose you could try a driving licence, but that might lead to more complications as Brits are supposed to get a Greek driving licence instead of a UK one. You will need a certified copy of the passport (by a lawyer)
6. Fee - I think it was €16.
I think that is all that they asked for. I went back about three times before I got it right - but that is about par for the course. If you do all the above you should become the proud owner of a digital residents permit.
Have I covered all your questions - I hope it is of some help to you. I was pretty reluctant to put my head above the parapet and admit that I live in Greece - in case I end up being taxed here. We also seem to get our passports stamped at customs now. The greek guy stamped mine but, being a friendly Greek, did not have any ink in the stamp - so not a mark on my passport. The officer in Frankfurt was, I fear, less friendly and more organised!