The larvae of the leaf miner moth, which has spread to Britain from Greece and Macedonia, burrows into the leaves of the horse chestnut tree, causing them to turn brown earlier than normal in August.

The condition can affect the size of conkers produced by the trees.

Aside from this moth problem, up to 41% of the nation’s estimated 11,100 horse chestnuts have so-called bleeding canker disease, according to the Forestry Commission’s investigation arm, Forest Research.