Small factoid.
There's two types of ELG depending on what time of the second world war your looking at.
Around 1940 the RAF bought a lot of land that would be useful as "scatter fields" that aircraft could bolt to in case of German invasion and their aerodromes were overrun. These were often tiny patches of grass just big enough for fighters with no facilities at all.
Easiest way to imagine it is the tented temporary aerodrome at the start of the Battle of Britain film.
These were marked on certain Air Ministry maps as "ELG" and some grass aerodromes are specifically named as Emergency Landing Grounds as a secondary use.
Couple of examples of ELGs as per the above I know about were at Temple Guiting and Turkdene in Gloucestershire and just to the west of the Burford Grammar school in Oxfordshire. RAF Northleach was designated as a ELG prior to them sorting the plumbing out so that Flying Training Command could use it proper.
Most of these scatter fields/ELGs were removed from maps by 1944 as the threat of invasion had passed.