On earth, a strange creed could be regressive (6)

I believe the answer is:

recede

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'be regressive' is the definition.
I can't judge whether this defines the answer.

'on earth a strange creed' is the wordplay.
'on' says to put letters next to each other.
'earth' becomes 'e' ().
'a strange' indicates an anagram.
'creed' is an anagram of 'reced'.
'e' put after 'reced' is 'RECEDE'.

'could' is the link.

Can you help me to learn more?

(Other definitions for recede that I've seen before include "Move backward" , "Decree (anag) - ebb" , "Go back, ebb" , "Start balding" , "Go backwards" .)

I've seen this clue in the Evening Standard.

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