Some feedback from an entomologist who looked at the photos:
“Did the photographer see the wasp attacking aphids? It’s hard to tell from the images, but at a guess I would say it is probably an Ichneumon wasp, most likely Diplazon laetatorius. If it is, then you can probably consider it as a pest in the garden. These wasps are parasites of hover flies, and the hover flies are likely feeding on the aphids.
“The hover fly maggot is large and clear, you can see their internal organs quite clearly. They are voracious predators of aphids and other small insects (including psyllids), and are considered beneficial organisms. The adult hover fly often looks much like a bee or vespid wasp (mimicry), and feeds mostly on nectar. We have looked into rearing hover flies in the past; however they are very difficult to rear.”