The most common and most likely answer to this crossword clue is the 7 plus 3 letter word DRUMMED OUT
I've seen this crossword clue in The Guardian
D
R
U
M
M
E
D
O
U
T
Buddy explains!
The straight part
We know that "Expelled from office" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expelled from office = drummed out.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.