The most common and most likely answer to this crossword clue is the 3 plus 6 plus 6 letter word NON COMPOS MENTIS
I've seen this crossword clue in The Times
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More clues leading to the result NON COMPOS MENTIS
- Rampant nepotism amongst junior officers is without reason
- Potty which is not up to being tried
- Maybe corporal punishment’s introduction sorted out sons with time? That’s insane!
- Not all there speaking in ancient language?
- NCO job consists of shutting up soldiers and barking
- Comments on poison, lacking nothing – mad? Out of one’s mind!
- Unable to focus on components I’m starting to solder imperfectly
- Not all there spreading nepotism among subordinate officers
- Officer and soldiers confined to station — one's gone upstairs
Buddy explains!
The straight part
We know that "gone upstairs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gone upstairs = non compos mentis.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.