A new tanaupodid mite, Lassenia newellisp. nov. is described based on a larva parasitising the aphid Myzocallis coryli (Goeze, 1778) (Aphididae) in Scotland, Great Britain. It is the ninth species of Lassenia known from the larval stage, the second host association for the genus and the first one for which the specific affiliation of both the parasite and its host is provided. The finding contributes to the taxonomy and biology of Tanaupodidae which have been considered to form one of the basal clades of Parasitengona. The discovery of elongate seta on the dorsal surface of tarsus III in L. newelli, a characteristic also shared by the monotypic Amphotrombium, supports the hypothesis of possible links between the tanaupodids and amphotrombiids as early derivative taxa of parasitengone mites.