On 2nd May 2017 the European Commission and the European Medicines Agency (currently based in London) issued a Q&A document. This first list of questions and answers addresses the establishment requirements (within the EEA), and will be updated.
The document is here. From 30th March 2019 00:00 hrs (CET) the UK will be a (EEA) third country, and the following provisions will apply :
(1) marketing authorisation holders must be established in the EEA (this includes Norway, Iceland and Liechtenstein),
(2) Qualified Persons for Pharmacovigilance (QPPV) must reside and carry out their tasks within the EEA,
(3) the Pharmacovigilance System Master File (PSMF) must be located within the EEA,
(4) active substances manufactured in the UK will be considered imported active substances,
(5) medicinal products manufactured in the UK will be considered imported medicinal products,
(6) batch release sites (for certification) must be located in the EEA.