Metallus albipes

At the time this sawfly mine (found during a Norfolk Moth Survey leafmining event) was identified as either Metallus albipes or Metallus pumillus, but according to my notes the larva clearly showed only two spots behind the head which would make it albipes. Although the larva is visible in the photo you can't really make out the spots here.

occupied mine of Metallus albipes, Lynford Arboretum (Norfolk, UK), 13th October 2018