Often seen in churchyards, these prog rockers drinking water were regularly ejected (3,5)

I believe the answer is:

yew trees

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'often seen in churchyards these' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'prog rockers drinking water were regularly ejected' is the wordplay.
'prog rockers' becomes 'Yes' (Yes are a progressive rock band).
'drinking' is an insertion indicator (inserted letters are consumed or drunk).
'regularly ejected' indicates alternate letters (letters removed at regular intervals).
'water'+'were'='waterwere'
The alternating letters of 'waterwere' are 'wtree'.
'yes' going around 'wtree' is 'YEW TREES'.

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I've seen this clue in The Independent.

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