The most common and most likely answer to this crossword clue is the 6 plus 8 letter word VESTED INTEREST
I've seen this crossword clue in The Guardian
V
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T
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D
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More clues leading to the result VESTED INTEREST
- Everest — it tends to be tricky, a matter of personal concern
- Personal stake revealed by setters – evident in cryptic form!
- Events set tried to get organised — reason for ulterior motive?
- Insecure teen’s tried on garment for personal benefit
- Setter’s evident bungling creates particular concern
- The banian manufacturer’s personal stake
Buddy explains!
The straight part
We know that "reason for ulterior motive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reason for ulterior motive = vested interest.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.