Confidence: It's likely to be this, but I can't be certain.
Notes: The key feature on this larva is the striking white dorsal stripe which is right for the suggested species. I've checked it against other Lithophane species in ukleps. It doesnt look like Blairs or Grey Shoulder-knot, Softly's SK isnt recorded in the north of Ireland, nor is Conformist, Nonconformist or Tawny Pinion. The larva was found crossing the road in hazel/blackthorn scrub. Pale Pinion looks likely- the adult was recorded near the site last Autumn. After all of the above, I hope it is a Lithophane.