Confidence: It's likely to be this, but I can't be certain.
Notes: Certainly a Crescent, very possibly the subspecies 'scotica' owing to location. "Subspecies scotica is smaller and darker than ssp. leucostigma and is more brightly marked" (Waring, Townsend and Lewington 2009). This specimen seems very dark and brightly marked as in the brightness of the trailing crossband.