This is one of the many species that belong to the ichneumon family, within the order that also includes bees wasps and ants. There are over 2000 species in Britain alone and many are hard to id easily - so I won't attempt to name it! They are parasitic in that they lay their eggs on host larvae or eggs of other species - often caterpillars. The ichneumon larva slowly devours the host from the inside and in many cases emerges from the host's pupa stage. I found an unknown pupa in the soil recently and kept it in a jar to see what would emerge... and got one of these!
They mostly have this narrow waist, slender body, long antennae and legs, and the size of the ovipositor for egg-laying, at the tail end varies among the species.
More to read here: http://en.wikipedia.org/wiki/Ichneumonidae
You're welcome. I saw one of these, or a very similar species, today in the garden. I've noticed it flying around a few times lately but for once it landed, allowing me to look it up and down briefly. In one of my books a species called Amblyteles armatorius looked like a good match, but it came with the caveat that there are several other similar looking species.
The name led me to this interesting article:
In the 4th paragraph it helpfully links to another site that demonstrates the variants on the yellow and black colour scheme and one or two other minor details one has to look for, assuming the critter keeps still long enough... Next time I see it I'll have to take a closer look!
It is a pleasure to see somebody exercising good grammar and spelling, and even italicising zoological names, while also being helpful, informative and friendly. Thank you for enhancing the quality of this forum.
(You'd think I was an admin!)