no it definitely wasn't shin splints, it was my ankles and bottom of my calves (back of my legs). it was more like a severe ache than cramp... it was weird as i run quite regularly and have never felt this before. it's also definitely not caused my my trainers as i have had them a while and they're proper running shoes. i am going for a run tonight, so will see if it happens again.
i was thinking what could have caused it- maybe that i had been wearing high heels a few days before (although this isn't out of the ordinary for me!), or that i hadn't had much to eat during the day so perhaps a lack of energy/low blood sugar?