Confidence: I'm as sure as I can be.
Notes: Found on Alder. The shape of the larval case combined with the food plant indicates this species. The photo with the dark background shows the first case which is 'pistol shaped'. As the larva grows it abandons his case and makes a second case which is straight and typically shows the serrations along the top edge which are the edge of the leaf from which the case was excised (shown in the picture with the lighter background). The larva excavates a mine in the leaf and in the second case photo the outline of the larva can be just about made out extended forward from its case inside the mine in front. This larva has moved several times and taken up positions on both the underside and upperside of leaves.