Confidence: It's likely to be this, but I can't be certain.
Notes: Overall length of this insect was 14mm. I believe it is a male of the suggested species due to its size and also its slender structure (females tend to be bigger but also more robustly constructed, broader due to having a larger abdomen). It was found at a small slightly acidic upland lake surrounded by blanket bog, which is the correct habitat. 'The adult Trichoptera of Britain and Ireland' by Barnard and Ross 2012 gives a forewing size of 9-15mm for a male and 13-16mm for a female. At 14mm this one would have had a forewing length of 12mm or so which isnt decisive for sexing but the slightness of its build would suggest a slender abdomened male.