It's an Acleris alright. Difficult to tell which one from the photo. It looks grey, so it could be sparsana.
It's definately grey, but the flight season in the books is Aug to Oct, so would be either v early (or late!) if it were sparsana...?
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From British Torticoid Moths for Acleris sparsana: "August to October, hibernating until the following spring (Williams, 1915: 220), specimens having been taken as late as the 25th May (Meldola, 1915: 198)."