While most pilots are aware that they will no longer be able to fly EASA aircraft (encompassing most new factory-built and classic US ‘Group A’ aeroplanes) on their old national PPL after 8 April, they should be aware that the CAA is warning that applications for the EASA licence should be submitted by 22 March to allow them to be processed by the deadline
From 8 April neither the old, non-expiring UK PPL, JAR-FCL PPL, nor an NPPL will allow you to operate an EASA aircraft type (although you will continue to be allowed to fly ‘non-EASA’ Annex II types such a homebuilts and vintage aircraft operating on a Permit to Fly, UK microlights and deregulated aircraft).
To fly EASA aircraft – for example common GA types such as the Cessna 152 or Piper PA-28 on an EU Part-FCL Private Pilot’s Licence (PPL) – you will need an internationally recognised Class 2 medical certificate obtained from an aero-medical examiner (AME).
There is a second option: if you want to fly EASA aircraft using an EU Part-FCL Light Aircraft Pilot’s Licence (LAPL) you will need a LAPL medical certificate. The LAPL medical assessment can be conducted either by your GP or an AME. The LAPL medical certificate is valid throughout the EU.
The medical requirements are spelled out in full here.
Details on the licence conversion can be found at this link.