The early larval stage mine elm leaves in autumn. Mines start from the midrib and head outwards along a vein, terminating in a small (c.2-3mm) elongated oval excision.  All frass is expelled from the mine, and can be seen along the midrib underneath.  The cut-out leaf in used to make a larval case in which it overwinters on an elm twig, resuming feeding in late spring.  These mines are large blotches with a small central hole through which the larva feeds. 

The adult moth has plain greyish-ochre forewing with a cream costal streak.

Coleophora badiipennella makes very similar leaf mines, but with larger excisions and frass retained in the mine. 

There are many similar adult Coleophora.

adult leafmine

Photograph leaf mine with backlight and underneath with natural light to show expelled frass. Measure the excision and include information in notes or photo.

Specimens of adult moths will need to be examined by an expert; dissection may be required

Elm

Mainly in south and south-east of England (ref: https://ukmoths.org.uk/species/coleophora-limosipennella/

Rarely recorded

http://www.leafmines.co.uk/html/Lepidoptera/C.limosipennella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/gelechioidea/coleophoridae/coleophora/coleophora-limosipennella/