Phil C wrote:...I could stay longer than 6 months but then I am into the tax game. Any advice on my understanding would be great.
I think people confuse physical residency and tax residency.
Physical residency is how long you are actually here in any one year. Under current EU law you are free to move around the EU but you are supposed to apply for an EU Residency Certificate if you stay longer than 3 months and that does have conditions attached. They are defined in the EU Directive which is then transposed into Greek law. Because there is free movement, subject to those conditions, it does not need to specify any "minimum stay" restrictions to qualify for the Residency Certificate. Say you wanted to stay for 5 months. That is longer than 3 months so you should get a Residency Certificate. If you then left for 7 months and came back again that Residency Certificate would still be valid. When the UK leaves the EU you will no longer be an EU citizen, so that Residency Certificate will not be valid, nor will you have the right of free movement. You will need to exchange the Residency Certificate for a third country biometric residency card. It is quite possible that the terms under which you can do that will have minimum residency rules or they might not. We simply don't know if there will be such rules or what they will be until an agreement is reached.
Tax residency is different. Under Greek law and under the terms of the UK-Greek Double Taxation Agreement someone is regarded as tax resident in the country where they spend more than 183 days. Clearly that is totally different from the rules for obtaining a Residency Certificate. Under current rules someone could quite legally hold a Residency Certificate and be tax resident in the UK. Whether that will still be true under whatever new agreement is signed we won't know until it is signed.
It is worth noting that some people live here permanently but still remain tax resident in the UK acting on the advice of their accountants. How their accountants are achieving this I am not certain. For those who have been here a long time, the Greek law used to be that you were tax resident where the majority of your income arose and, for UK pensioners at least, that was normally the UK. It is possible that their accountants registered them as tax resident in the UK quite legally when that law applied and have simply kept quiet when the law changed. I believe one accountant is using a clause in the tax law that says the 183 day rule doesn't apply under certain conditions. If you read the law it is debatable if that was intended to apply long term, i.e. it meant that you might be in Greece for more than 183 days in one particular year and not be tax resident because of those exemptions but not year after year. I know some accountants are simply stating that their clients are here for less than 183 days each year even though they are here permanently. A terminological inexactitude, to use the phrase coined by Winston Churchill.