Major trouble, having registered ever-watchful presence (3,7)
I believe the answer is:
big brother
'ever-watchful presence' is the definition.
I can't tell whether this definition defines the answer.
'major trouble having registered' is the wordplay.
'major' becomes 'big' (I've seen this in other clues).
'trouble' becomes 'bother' (synonyms).
'having' is an insertion indicator.
'registered' becomes 'R' (abbreviation, as in registered trademark).
'bother' placed around 'r' is 'brother'.
'big'+'brother'='BIG BROTHER'
Can you help me to learn more?
(Other definitions for big brother that I've seen before include "He was watching you (Orwell)" , "Orwellian dictator - TV show" , "Personification of a totalitarian state" , "A relatively large" , "TV programme" .)