The most common and most likely answer to this crossword clue is the 14 letter word NORTHUMBERLAND
I've seen this crossword clue in Independent
N
O
R
T
H
U
M
B
E
R
L
A
N
D
Buddy explains!
The straight part
We know that "border area" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case border area = northumberland.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.