The most common and most likely answer to this crossword clue is the 8 letter word INSISTED
I've seen this crossword clue in Financial Times
I
N
S
I
S
T
E
D
More clues leading to the result INSISTED
- Demanded I vigorously dissent
- Was firm in position to accept small donation initially?
- Maintained tidiness after having a shift around
- … repeated problem with stone inside
- Maintained it’s Enid’s move
- Firmly maintained orderly tidiness
- Demanded tidiness for a change
- Urged dissident to yield after abdicating crown
Buddy explains!

The straight part
We know that "Maintained" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case maintained = insisted.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.
What does INSISTED mean?
INSISTED verb- (with on or upon or (that + ordinary verb form)) To hold up a claim emphatically.
- (sometimes with on or upon or (that + subjunctive)) To demand continually that something happen or be done.
- To stand (on); to rest (upon); to lean (upon).