Confidence: I'm as sure as I can be.
Notes: There are 5 Oecetis caddisfly species covered in 'The adult Trichoptera of Britain and Ireland', Barnard and Ross 2012. Male O. ochracea have forewing lengths of 10-13mm (the female is smaller). This size is correct for the above insect, none of the other 4 species have wing lengths as big as this, the other 4 are under 10mm in size of forewing. These are very common on small upland lakes in this area in mid/late summer. They ahve very long antennae.