The wasp is a species of Ichneumonidae, of the subfamily Ichneumoninae. These are parasitoids of Lepidoptera pupae; they lay an egg in either the caterpillar or the pupa (depending on the species) and then emerge from the pupa of the host. As for the species, this is a nice case of perpetuating errors. It’s certainly not Ichneumon suspiciosus, it is obviously not the same species as that in the Flickr photo, which is certainly not Ichneumon suspiciosus either! Although quite a few species of Ichneumoninae can be identified from good photos, I don’t think many people appreciate the nature of the differences that are used to distinguish between species. For example, Ichneumon suspiciosus females have a conspicuously red-banded abdomen with a big white spot at the apex, as do numerous other species; this specimen is basically black whilst the specimen on Flickr is black with a white spot on the scutellum. There are about 365 species of Ichneumoninae in Britain and many of the larger species have a white spot on the scutellum, so that’s not too helpful. Most species also share the same sort of build and proportions. A lot of the confusion stems from the fact that the popular field guides illustrate very few species of Ichneumonidae so people are not aware of the diversity of the group and thus apply one of the few names from field guides to the very many different species that are photographed and put online. And as to what this ichneumonid is, it’s very difficult to be sure from the photo but, of the small number of large, all-black species, Stenichneumon culpator is the most common.
All the best,