The most common and most likely answer to this crossword clue is the 2 plus 7 plus 3 plus 1 letter word MY HUSBAND AND I
I've seen this crossword clue in The Guardian
M
Y
H
U
S
B
A
N
D
A
N
D
I
Buddy explains!
The straight part
We know that "Leading pair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leading pair = my husband and i.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.