The most common and most likely answer to this crossword clue is the 9 letter word REGULARLY
I've seen this crossword clue in The Daily Telegraph
R
E
G
U
L
A
R
L
Y
Buddy explains!

The straight part
We know that "on a frequent basis" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case on a frequent basis = regularly.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 REGULARLY mean?
REGULARLY adverb- With constant frequency or pattern.
- Normally; ordinarily.