The most common and most likely answer to this crossword clue is the 12 letter word HIGH-RANKING
I've seen this crossword clue in The Times
H
I
G
H
-
R
A
N
K
I
N
G
More clues leading to the result HIGH-RANKING
Buddy explains!
The straight part
We know that "at the top" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at the top = high-ranking.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 HIGH-RANKING mean?
HIGH-RANKING adjective- At an important, elevated, or exalted level in a hierarchy or organization; high-level.