The most common and most likely answer to this crossword clue is the 14 letter word CONTRAVENTIONS
I've seen this crossword clue in The Daily Telegraph
C
O
N
T
R
A
V
E
N
T
I
O
N
S
Buddy explains!

The straight part
We know that "Offences" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case offences = contraventions.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.
Crossword Answer definitions
CONTRAVENTIONS noun- The act of contravening a rule, regulation, or law, or of not fulfilling an obligation, promise, or agreement.