The most common and most likely answer to this crossword clue is the 7 plus 7 letter word PRIVATE MEMBERS
I've seen this crossword clue in The Guardian
P
R
I
V
A
T
E
M
E
M
B
E
R
S
Buddy explains!
The straight part
We know that "those taking a back seat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case those taking a back seat = private members.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.