Hello Nick
You need to have the sort option on the subcategories. See the changes I did for HMCG Alnmouth and HMCG Lyddon Spout .
On the HMCG Lyddon Spout category I did the following change. [[Category:HM Coastguard Stations]] was changed with a pipe character | and then I added three letters after it to help with sorting. It now reads [[Category:HM Coastguard Stations|Lyd]]