Confidence: It's likely to be this, but I can't be certain.
Notes: Basal two postpetiolar tergites almost entirely yellow, rest of gaster almost entirely black, giving the appearance of a single broad yellow band. This is a common colour pattern for many species of Ichnuemon, including I. xanthorius (males); I. extensorius (males); I. stramineus (males and females); I. terminatorius (males and females). Definitely not Amblyteles armatorius which has a different colour pattern: has a series of narrow yellow apical bands in the female, e.g. http://www.ispot.org.uk/node/86404 or two irregular yellow bands in the male, e.g. http://www.ispot.org.uk/node/224563.