The most common and most likely answer to this crossword clue is the 15 letter word TWELVEÂ APOSTLES
I've seen this crossword clue in The Guardian
T
W
E
L
V
E
Â
A
P
O
S
T
L
E
S
Buddy explains!
The straight part
We know that "faithful followers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case faithful followers = twelve apostles.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.