The most common and most likely answer to this crossword clue is the 8 letter word ROOFTREE
I've seen this crossword clue in Financial Times
R
O
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F
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More clues leading to the result ROOFTREE
Buddy explains!

The straight part
We know that "high level support" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case high level support = rooftree.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 ROOFTREE mean?
ROOFTREE noun- The primary beam of a roof, ridgepole; hence, the roof.
- A home; household.