From 2012 people paying tax in the UK, but living in Greece#, will be required to complete a RESIDENT CERTIFICATE issued by the UK tax office. This form needs to be completed (and sent to your accountant) before April 2013, in order to file correctly for the year 2012. ’
Even if you have very little Greek income, it seems this form needs to be completed, or you will be taxed in Greece on your Global income, as a permanent resident of Greece. ie all your income will be assumed to be Greek unless you can prove otherwise! It appears that the Greek Government is now assuming that anyone with a house in Greece is a permanent resident!
http://www.hmrc.gov.uk/news/cert-of-residence.htm
http://www.hmrc.gov.uk/news/cert-of-residence.htm

