The most common and most likely answer to this crossword clue is the 12 letter word FIGURATIVELY
I've seen this crossword clue in The Daily Telegraph
F
I
G
U
R
A
T
I
V
E
L
Y
Buddy explains!

The straight part
We know that "a manner of speaking" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a manner of speaking = figuratively.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 FIGURATIVELY mean?
FIGURATIVELY adverb- (manner) In a figurative manner.
- Used to indicate that what follows is to be taken as a figure of speech, not literally.