That is only for NON-EASA aircraft...
The Medical Declaration is an affirmation of your medical fitness to fly and to exercise the privileges of either a:
•EU Part- Flight Crew Licensing (FCL) Private Pilot Licence (PPL) to fly non-EASA aircraft,
•EU Part-FCL Light Aircraft Pilot Licence (LAPL) to fly non-EASA aircraft,
•National Private Pilot Licence (NPPL),
•UK Private Pilot Licence (UK PPL), or a
•UK Commercial Pilot Licence (CPL) Balloons that is restricted to commercial operation and the privileges of a UK PPL (Balloons and Airships).
Further down the page it states...
Flying EASA Aircraft
You cannot use a medical declaration to fly an aircraft that has an EASA certificate of airworthiness or permit to fly, unless you possess an EU Part-FCL PPL or a LAPL with an appropriate medical for that aircraft at the time of the flight. EU Part-FCL PPL holders will need an EU Class 2 Medical Certificate. LAPL holders will need a LAPL medical certificate.
There is an EU exemption that allows UK national licence holders to fly certain EASA aircraft until April 2018 that is limited to sailplanes, balloons and visual flight rules (VFR) flight in single engine piston aircraft no greater than 2000 kg MTOM with a maximum of 3 passengers.
This is where all the confusion lies ... the date therein about Self Dec for EASA aircraft still states April 2018, but that was amended at the 11th hour last year to April 2019, and hence my query which Irv has answered and pointed to a doc that now says April 2020
It really is no wonder people ‘get it wrong’ and are accused of not reading and understanding the regs ... apart from Irv’s link, doing a search brings up very little about dates for self Dec for LAPL and EASA aircraft that is correct.