The most common and most likely answer to this crossword clue is the 11 letter word CONTRADICTS
I've seen this crossword clue in The Daily Telegraph
C
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More clues leading to the result CONTRADICTS
Buddy explains!

The straight part
We know that "Denies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case denies = contradicts.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 CONTRADICTS mean?
CONTRADICTS verb- To deny the truth of (a statement or statements).
- To deny the truth of the statement(s) made by (a person).
- To be contrary to (something).
- To give an order contrary to (another order or wish), oppose (something).
- To give an order contrary to one given by (another person), oppose or resist (someone).
- To speak against; to forbid.