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I was going to suggest E. similis on the basis of these passages from Stubs and Falk (British Hoverflies):

E. tenax: "... differs from pertinax in the presence of a dark front tarsus, and from both pertinax and similis by the stripes of dark hair down the eyes, the almost completely dark hind tibia with long hairs on the dorsal and ventral surfaces, and the very broad black face stripe."

E. Pertinax: "... has an entirely orange front tarsus (unlike [tenax and similis]) and the hind tibia is pale in the basal half (unlike tenax)."

E. similis: "... the front tarsus is black (entirely yellow in pertinax), the face is extensively dusted (tenax has a wide black facial tripe) and the hind tibia is broadly pale at the base (like pertinax but unlike tenax)."

They have E. nemorum as a synonym of E. interruptus. I will go and look it up.