Eriocrania semipurpurella

Wingspan 10 to 16 mm. The adults are difficult to tell apart from E. sangii without reference to the genitalia structure, but the larvae are quite different, semipurpurella being white or yellowish, sangii being quite dark grey. 

Adult Leafmine with larva

Adult: Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

Leafmine and larva: Unless identified by a recognised expert, photos are required showing the mine (preferably backlit to show frass) and the larva which should be removed from the mine for the purpose of photography.

Where Birch is present.

The adults fly in March and April, especially in sunshine.

The larva mines in a Birch leaf, forming a large blotch, from March to May.

The commonest and most widespread of the Eriocrania species that feed on birch, occurring throughout most of Britain. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as common.

Infrequent, though possibly under recorded in Leicestershire and Rutland.

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