Wingspan about 14 mm.  The larva mines the leaves of Poplar species, making a short corridor along midrib and often into the side vein; they then feed on the leaf under-surface inside a silken tube covered in frass.  The larva is red-brown, which helps to distinguish from Gypsonoma dealbana.

Gypsonoma dealbana makes similar feeding signs on poplars 

Adult leafmine+larva

Only tenanted mines can be recorded.  Photograph the mines on leaf under-surface, and the larva.

In areas where Poplars occur.

Flies during June and July in a single generation.

The larva feeds on Poplar (Populus), initially grazing the underside of a leaf, from within a silken tube which becomes covered with frass.

A relatively local species, occurring sporadically throughout England. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as Nationally Scarce B.

It appears to be uncommon in Leicestershire and Rutland, where there are few records. L&R Moth Group status = D (rare or rarely recorded).

http://www.leafmines.co.uk/html/Lepidoptera/G.oppresana.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/apoditrysia/tortricoidea/tortricidae/olethreutinae/eucosmini/gypsonoma/gypsonoma-oppressana/#:~:text=The%20young%20larva%20makes%20a,causes%20under%2Dsurface%20window%20feeding.