The most common and most likely answer to this crossword clue is the 14 letter word UNSTANDARDISED
I've seen this crossword clue in The Sunday Telegraph
U
N
S
T
A
N
D
A
R
D
I
S
E
D
Buddy explains!
The straight part
We know that "not uniform" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not uniform = unstandardised.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.