The most common and most likely answer to this crossword clue is the 11 letter word AFFECTATION
I've seen this crossword clue in The Daily Telegraph
A
F
F
E
C
T
A
T
I
O
N
Buddy explains!

The straight part
We know that "Deliberate pretence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case deliberate pretence = affectation.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 AFFECTATION mean?
AFFECTATION noun- An attempt to assume or exhibit what is not natural or real; false display; artificial show.
- An unusual mannerism.