And no sooner said than done - our ichneumonid specialist (who is at the sharp end of that group of 4-6) comments thus:
It’s Callajoppa cirrogaster – indeed one of our showier ichneumonids. It’s a parasitoid of hawk-moths, such as Smerinthus (Eyed Hawk-moth) and Laothoe (Poplar Hawk-moth). They emerge from the pupa but oviposit into the host when it is a larva. Nice photo!