I have seen the damage to Horse Chestnut leaves, caused by the leaf miner, in other parts of the country. The trees look drab as all the leaves turn papery yellow as they are eaten from the inside by the grub.
I can't say I have noticed any problems locally (have you?) until the other day when I noticed a Horse Chestnut in Todmorden with similar blotchy leaf symptoms.
The leaf miner doesn't kill the tree but can severly weaken it and make it more susceptible to the effects of Bleeding Canker, which is killing thousands of HC's in England.
We have lost many Horse Chestnut trees in Tod from this bleeding canker and it could soon become quite a rare species.