---

cristata is known from Geometrids on broadleaved trees, so that is a bit difficult on the Shetlands.

Geniculata is well known from Tipulidae larvae.
So given the biology, that is your candidate.
I do stress this is not an ID from picture.

In dutch, we have this family Geenidae, which would translate in English to the superfamily Noidea
Very common, many Siphona belong here.

Theo