Environmentalists protect ancient grassy area (10)

I believe the answer is:

greensward

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'grassy area' is the definition.
(greensward means grass-covered ground)

'environmentalists protect' is the wordplay.
'environmentalists' becomes 'greens' (members of the Green Party).
'protect' becomes 'ward' (warding is a kind of protecting).
'greens'+'ward'='GREENSWARD'

'ancient' acts as a link.
This may not be right. It may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for greensward that I've seen before include "mostly turf" , "Lawn" , "Grass covered ground" .)

I've seen this clue in The Times.

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