The documents issued to UK nationals before the end of the transition period under Greek Presidential Decree 106/2007 are the Registration Certificate of Citizen of Member State of EU and the Permanent Residence Document of Citizen of Member State of EU.
Given that Union law ceases to be applicable to and in the United Kingdom as of 1st January 2021, the aforementioned documents:
-cease to be valid as 1st January 2021, as their legal basis automatically ceases to apply to UK nationals, as third-country nationals.
-remain in the possession of the persons concerned, as they can be used as proof of exercising the right of residence in accordance with Union law before the end of the transition period. They are retained by the competent Authorities, only when they are submitted by the applicant as a supporting document for the proof of their residence status before the end of the transitional period in the context of the application for the residence document under article 18 (4) of the WA.
-can not be decisive for the residence status under WA. This means that there is no unconditional exchange of the residence document under EU law with the new residence document under the WA. In any case, the persons concerned should meet the conditions set out in the WA in order to be beneficiaries of it.
-can be showed to border guards at the external Schengen borders to prove that the holder has the right to reside in the Schengen area without internal border controls and as a result, no visa is required.
-can be showed to officers of public Authorities and KEP as proof of their residence status under the Withdrawal Agreement in their transaction with them (for more information, click here)
