The most common and most likely answer to this crossword clue is the 6 plus 6 letter word HIDDEN AGENDA
I've seen this crossword clue in The Sunday Telegraph
H
I
D
D
E
N
A
G
E
N
D
A
More clues leading to the result HIDDEN AGENDA
- Meeting might not proceed before locating this ulterior motive
- Ulterior motive: what collagen database has in it?
- Subtext that’s in thread, negatively reversed?
- Undisclosed reason Dad had engine fixed?
- Secret plan suggested by Häagen-Dazs?
- Engine dad had designed for secret purpose
- Dad had engine modified showing ulterior motive
- Ulterior motive that could delay the meeting?
- What we see in Copenhagen — Danes’ ulterior motive
- , 8. Feature of Copenhagen — Danish design kept secret
Buddy explains!
The straight part
We know that "reason kept secret" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reason kept secret = hidden agenda.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.