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This species is associated with damp places and was seen at the same location at about the same time last year (Search terms: Stockway Kelisia punctulum).
It seems a fairly stable part of this particular environment, as the pond dried up in the summer just past.
It is impressive what they can survive - but then, they're dependent on the plants, rather than the habitat, so as long as the sedges can find water below ground then there's no reason for the hopper to struggle.
It's worth noting that Kelisia is a difficult genus, but I'm sure you're right with this one - that dark medial vein on the wing seems to be diagnostic when combined with the lack of other markings.
Lat/Lng: 51.4337, -2.7624
OS grid ref: ST470707