Athalia circularis

The old RES key has this as Athalia lineolata which is, I think, a synonym of circularis. I note from sawflies.org.uk that this species may in fact be a complex of species differentiated by foodplant.

This one (swept from among Bluebells) was keyed using the RES key. Until I examined the saw I wasn't convinced which way to go at the couplet that eliminated cordata - at some angles the clypeus looked very shiny and the hairs were hard to see which suggested cordata, but at other angles you could see plenty of hairs (albeit never as dense as on the labrum). The underside of the thorax had a broad orange centre - more than I would expect for cordata where it should be "entirely or almost entirely black" - so this pointed more towards circularis. The shallow teeth on the saw cleared up the confusion - far too shallow for cordata and spot on for circularis.

female Athalia circularis showing wings, underside of head/thorax and close-up of clypeus and labrum and two zooms of the saw, Old Carr near Gressenhall (Norfolk, UK), 30th April 2022