Cameraria ohridella

An adventive species mining horse-chestnut, usually in considerable numbers, and almost always present wherever the foodplant occurs, even where planted singly; as of 2018 it was still possible to find isolated trees in remote parts of Exmoor which had not been colonised by the moth.  Commonest in urban areas, likely to be altogether absent in areas of the countryside where no horse-chestnuts are present.