Swans crowding over English island mostly common knowledge? (4,6)
I believe the answer is:
open secret
'swans crowding over english island' is the definition.
I can't judge whether this defines the answer.
'mostly common knowledge?' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'common knowledge?' becomes 'opensecrets' (I've seen this in another clue).
'opensecrets' with its last letter removed is 'OPEN SECRET'.
Can you help me to learn more?
(Other definitions for open secret that I've seen before include "Everyone knows it" , "Centre pose (anag.)" , "Generally known matter" , "common knowledge" , "Private matter actually known to many" .)