Re Morale, In SC2* there is an entry in the victory conditions scripts with this format (below all the trigger, alignment, date, map position stuff) :
; #NATIONAL_MORALE_TRIGGER= Under what national morale situation will this event occur
; Format: country_id [national_morale_percentage] [above_or_below] (above_or_below values range [0, 1]; Above=1; Below=0)
If you wanted to have a victory condition where say UK (Nation ID =1) had <10% morale, you would enter that as:
#NATIONAL_MORALE_TRIGGER= 1  
(where the 1 represents UK, 0 represents "below 10%")
Just by looking through the files in WWI and my experience with the Civil War mod, it appears most NM-based surrenders are tied to a dummy decision event (basically a forced AI "yes" given under a certain condition), and activated by a Surrender 2 event with the "dummy=yes" condition. If you wanted to force a full surrender I could explain this further but it probably isn't necessary in your mod's case - all that would happen is the map would change colour and then the victory screen (and for battle of Britain, it isn't like the UK is being invaded anyway!).
*Note I haven't spent much time with SC3's editor (prefer the old game personally), so something might have changed in the new release. Unfortunately my time spent in SC2's editor won't be much help in that case.