To help those trying to figure this out (like me!), the full guidance on the CAA website is:
Self-declaring your medical fitness using the Pilot Medical Declaration
Once you have a licence, if you only want to fly UK (G) registered aircraft in UK airspace you can use the online Pilot Medical Declaration (PMD).
A medical declaration (from 25th August 2016) is an affirmation of your medical ‘fitness to fly’ and may be used to exercise the privileges of a:
• UK Part-FCL Private Pilot Licence (PPL) to fly UK (G) registered Part 21 and non-Part 21 aircraft;
• UK Part-FCL Light Aircraft Pilots Licence (LAPL) to fly UK (G) registered Part 21 and non-Part 21 aircraft;
• UK Part-SFCL Sailplane Pilot Licence (SPL) to fly UK (G) registered Part 21 and non-Part 21 aircraft;
• UK Part-BFCL Balloon Pilot Licence (BPL) to fly UK (G) registered Part 21 and non-Part 21 aircraft but restricted to private and commercial operation only (excluding commercial passenger ballooning, commercial operation only if commercial operation rating held).
• NPPL (NPPL) to fly UK (G) registered non-Part 21 aircraft;
• UK PPL to fly UK (G) registered non-Part 21 aircraft; and
• A UK Commercial Pilot Licence (CPL) Balloons that is restricted to commercial operation and the privileges of a UK PPL (Balloons and Airships).
It is valid for flying with the following operational conditions;
• With not more than three passengers on board;
• in aircraft with a Maximum Take-Off Mass (MTOM) of 5700kg or less
• In Visual Meteorological Conditions (VMC) or when exercising the privileges of an Instrument Meteorological Conditions (IMC)/Instrument Rating (Restricted). The privileges of a full Instrument Rating (IR) are not applicable.
• by day or night when exercising the privileges of a Night Rating provided that colour safety has previously been checked by an AME.
• PMDs are not valid outside of UK airspace, as it is not an internationally-recognised medical standard, unless permission has been granted by the State of the airspace you are flying in.
Pilots must not make a pilot medical declaration if they do not reasonably believe that they meet the medical requirements for a Group 1 (Car) Licence issued by the Driver and Vehicle Licensing Agency and;
Holders of UK national licences only, to only fly aircraft no greater than 2000 kg MTOM
You may fly an aircraft no greater than 2000kg MTOM, provided you are not taking medication for any psychiatric illness. If you are taking medication for a psychiatric illness you must consult an AME and apply for a LAPL medical certificate, or
Holders of UK national and Part-FCL Licences, to fly any aircraft less than 5700kg MTOM
Do not suffer from any physical or mental condition or illness, or any history of such a condition or illness that might impair the safe operation of normal flight controls or render the licence holder unfit at any time to perform any function for which the licence is granted. As a minimum, such conditions include:
(a) any alcohol or drug abuse, addiction or misuse;
(b) any neurological condition requiring medication;
(c) any functional disability likely to impair safe operation of normal flight controls;
(d) any recent surgery or new medical treatment;
(e) any collapse, fainting (syncope), seizure or loss of consciousness;
(f) any history of (a) to (e); or
(g) other medical conditions specified by the CAA:
i. Being prescribed medication for any psychiatric illness
ii. Bipolar disorder, schizophrenia or other psychotic illness, or a diagnosis of personality disorder
iii. Dementia or cognitive impairment
iv. Being prescribed medication or treatment for angina or heart failure
v. Cardiac surgical procedures including coronary angioplasty or stenting and cardiac device implantation
vi. Insulin treatment for diabetes
vii. Chronic lung disease with shortness of breath on exertion
If any of the above are present the applicant must visit an AME and apply for a LAPL or Class 2 medical certificate (as appropriate to the privileges that they are seeking to exercise)