The most common and most likely answer to this crossword clue is the 6 plus 6 letter word LABOUR LEADER
I've seen this crossword clue in The Guardian
L
A
B
O
U
R
L
E
A
D
E
R
More clues leading to the result LABOUR LEADER
Buddy explains!
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.