Early Mason Wasp Ancistrocerus nigricornis

I keyed this using the RES Handbook to the Vespoid Wasps by M E Archer, the first time I've used this key other than checking Commmon and German Wasps. It keyed reasonably straightforwardly once I'd got my head round what the various surfaces and slopes on the first two gastral segments were referring to.

Early Mason Wasp Ancistrocerus nigricornis showing wings, jugal lobe of hindwing (as this wasn't visible in the previous photo), first gastral tergite and first and second gastral sternites (4 views), North Elmham (Norfolk, UK), 7th May 2023