A leaf mine on Common Nettle, Urtica dioica. I can;t find anything for Nettle on line that resembles this mine.
No interactions present.
It was among sting-ridden leaves in a clump of nettles, though it could have been something else. I did notice that my photo doesn't show any stinging hairs.
Lat/Lng: 51.395721, 0.07909
OS grid ref: TQ447683