Parliamentry Response to question
On 25th April, Chris Grayling The Secretary of State for Transport said
Quote: During the time-limited implementation period, the UK will no longer be an EU Member State. However, as set out in the terms of the agreement, common rules will remain in place. The EASA basic regulation will therefore continue to apply, so all UK-issued certificates, approvals and licences will be automatically recognised as valid in the EASA system (and vice versa).
As the Prime Minister made clear in her speech last month, beyond the implementation period we will want to explore with the EU the terms on which we could remain part of the relevant agencies, such as EASA. This will form part of the negotiations with the EU and Member States on how best to continue cooperation in the field of aviation safety and standards post-exit. Endquote
There is also a very informative and balanced paper that examines the options- available from the Royal Aeronautical Society
RAeS Civil Aviation Regulation- What Future after Brexit? published September 2017.