The most common and most likely answer to this crossword clue is the 6 plus 6 letter word DOUBLE DECKER
I've seen this crossword clue in The Sunday Telegraph
D
O
U
B
L
E
D
E
C
K
E
R
More clues leading to the result DOUBLE DECKER
Buddy explains!
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 DOUBLE DECKER mean?
DOUBLE DECKER noun- A vehicle (usually a bus, coach or train) or aircraft with two floors.
- A frigate with two decks above the waterline.
- (figuratively) Any object with two layers or parts stacked on top of each other.