I finally figured out that it's best to lure a dragon away from a village before fighting it (so I had been pretty daft for a while) but this particular legendary dragon would not die. It seemed much more powerful than any other I had fought, and I kept running out of health and magic, and having to literally run for the hills. I tried every combination of spells and shouts including Dragon Aspect, and after what seemed like hours, I got the blasted creature on the ground and threw fireballs at it from a great distance. It was touch and go who would die first.
It was only after I got back to Lakeview and looked for my enchanted alchemy gear for making some more potions, that I realised I was wearing it...