By far the most common leaf miner around here is the micromoth Stigmella aurella. Virtually every Bramble plant has a few leaves carrying one or more mines. This week I found a mine on Herb Bennet - Geum urbanum - and it immediately looked like a Stigmella mine: a long, sinuous mine with a central frass line:
A quick check revealed that Stigmella aurella mines Geum, too.
Compare the mine with the Bramble version Here.
Note that the mine on Geum is formed quite differently from that on Bramble. The thicker Bramble leaf-veins clearly have more impact on the route of the mine.