The most common and most likely answer to this crossword clue is the 9 letter word EQUERRIES
I've seen this crossword clue in The Guardian
E
Q
U
E
R
R
I
E
S
Buddy explains!

The straight part
We know that "aides in high places" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case aides in high places = equerries.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EQUERRIES mean?
EQUERRIES noun- An officer responsible for the care and supervision of the horses of a person of rank.
- A personal attendant to a head of state, a member of a royal family, or a national representative.