I first noticed these strange rolled-up leaf edges about a week ago, in the lane behind my house, and, since then, I’ve seen them in several places locally.
The plant is Red valerian (Centranthus ruber) and the leaf-rolls are galls, almost certainly caused by the larvae of a little bug called Trioza centranthi. The gall is where it makes its home until it matures into an adult bug, and you can see some of the larvae in the lower right photo below.
Amazingly, I photographed the little bug (see below) on one of the plants and I think this is the adult. I’ve read that Trioza centranthi is quite uncommon and, certainly, there are only 3 records in Aderyn, the Welsh biodiversity database but I imagine this is to do with under-recording rather than rarity.