Try comparing against these two:
Field Wood-rush
Heath Wood-rush
Its hard to tell from your photo but in comparison to the surrounding vegetation it looks very tall for Field Wood-rush but I must admit I'm used to seeing it growing amongst close sheep-cropped grasses. The straight flower stalks suggest Heath Wood-rush to me but on the other hand there don't seem to be enough flower heads for Heath Wood-rush. So in conclusion
If you can get back to it, have a look for rhizomes or stolons coming out from the base of the plant. Field Wood-rush has them Heath Wood-rush only very rarely does.