The most common and most likely answer to this crossword clue is the 8 letter word REFUTING
I've seen this crossword clue in The Sunday Telegraph
R
E
F
U
T
I
N
G
Buddy explains!

The straight part
We know that "Denying" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case denying = refuting.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 REFUTING mean?
REFUTING verb- To prove (something) to be false or incorrect.
- To deny the truth or correctness of (something).