The most common and most likely answer to this crossword clue is the 7 plus 1 plus 10 letter word INSPIRE A GENERATION
I've seen this crossword clue in The Guardian
I
N
S
P
I
R
E
A
G
E
N
E
R
A
T
I
O
N
Buddy explains!
The straight part
We know that "Mantra of 2012" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mantra of 2012 = inspire a generation.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.