Elachista regificella

Wingspan about 9 mm.  A rather attractive little species, sporting silvery metallic fasciae against a dark fuscous forewing, the central fascia being a (sometimes broken) elongated spot.  The larva mines the leaves of Wood-rush species forming a blister mine that often causes the leaf blade to pucker

Other species of Elachista may mine Luzula. Several speces of fly feed in leaf-mines on Luzula; feeding damage can be caused by a range of invertebrates. 

Adult Leafmine

Adult: Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.

Leafmine: please provide a backlit photograph of the leafmine and state the host plant species.

Their favoured habitat is open woodland where the larval foodplants Wood-rush (Luzula sp.) are present.

Adult moths fly in July

Single-brooded.  The larval foodplants are various Wood-rush (Luzula spp.).

It has a fairly wide, though scattered distribution over much of the British Isles, and can be scarce outside of the southern half of England. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as Nationally Scarce B.

Rarely recorded in Leicestershire and Rutland. 

http://www.leafmines.co.uk/html/Lepidoptera/E.regificella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/gelechioidea/elachistidae/elachistinae/elachista/elachista-regificella/