Even when it's pouring and I am down town shopping I still have an eye on the undergrowth and today paid off. A horse Chestnut at the car park bridge was covered in Leaf-mines. There is only one species that leaf-mines Horse Chestnut and that's Cameraria ohridella [Horse Chestnut Leaf-miner].
It was first recorded in the UK in 2002 and has rapidly spread north and west and is regarded as a pest species. I think its new for the valley, but Sid will confirm later. [New for Valley].