The most common and most likely answer to this crossword clue is the 8 letter word RHYTHMIC
I've seen this crossword clue in The Guardian
R
H
Y
T
H
M
I
C
Buddy explains!

The straight part
We know that "on a regular basis" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case on a regular basis = rhythmic.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 RHYTHMIC mean?
RHYTHMIC adjective- Of or relating to rhythm.
- Characterized by rhythm.
- Written in verse, especially rhyming verse.
- With regular, repetitive motion or sound.