Airspace restrictions and UAS geographical zones
Know what you are flying into
Most airspace a drone pilot must avoid is controlled airspace - in UK terms Classes A to E - comprising airways, control areas (CTA) and control zones (CTR). Around aerodromes you will also meet the ATZ (a cylinder around an aerodrome, roughly 2 nm radius to 2,000 ft) and the military MATZ. Elsewhere there are danger areas (D), restricted areas (R), prohibited areas (P), high-intensity radio transmission areas, parachute drop zones, glider sites and low-flying military routes. Temporary restrictions arrive by NOTAM - airshows, royal movements, emergency scenes, major events.
UAS geographical zones
Under the retained Regulation (EU) 2019/947, the CAA may designate UAS geographical zones that prohibit, restrict or attach conditions to drone flight. The best-known is the flight restriction zone (FRZ) around protected aerodromes - typically a 5 km radius around the aerodrome plus runway-end extensions, within which you need permission from the aerodrome/ATC. Do not assume an FRZ is only for international airports; any aerodrome can be designated protected.
Traps: 'I checked the map this morning, so I am fine' - NOTAMs change hourly. And 'the app showed no red circle' - the app may show only some zones, and geo-awareness data can lag.
Rule of thumb: before selecting a site, run two checks - is there any aerodrome within about 5 km (look for runways, hangars, circuit traffic), and is there a NOTAM or temporary restriction today? If you can see a runway or hear turbine aircraft, assume you are in somebody's airspace until proven otherwise.