The most common and most likely answer to this crossword clue is the 6 plus 6 letter word MOLLIE SUGDEN
I've seen this crossword clue in The Guardian
M
O
L
L
I
E
S
U
G
D
E
N
Buddy explains!
The straight part
We know that "in Are You Being Served?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in are you being served? = mollie sugden.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.