Confidence: It's likely to be this, but I can't be certain.
Notes: It looks like one of the taller variants of Carex nigra, but the photo isn't quite close enough for counting stigmas- should be in twos, whereas they are in threes in other sedges - but this is not always an easy character when stigmas break off or stick together, or both. Certainly a sedge, not a grass. N.B. I have never heard Phleum pratense being called "Black-grass". Usually Common Cat's-tail or Timothy.