As I was saying, there is no shame in making an honest mistake or two and PH has just pointed out to me that the picture of what I thought was a Juniper Shieldbug is in fact a Birch Shield Bug. The two are quite different, so I'm not sure where I went wrong there. The Juniper Shieldbug is much larger (ahem, actually smaller - I misquoted the fact sheet mentioned below, as PH has pointed out to me) and has distinctive pinkish-red curved markings on the corium. He has also pointed out that the dianostic feature used to separate these two species in the keys is that the first antennal segment in Elasmostethus (Cyphostethus) tristriatus(Juniper SB) does not reach the apex of the clypeus (front of the head), whereas in Elasmostethus interstinctus (Birch SB) it reaches beyond.
It may have had something to do with wanting to finish my piece for this forum before going to watch something on the box - or may be I simply misinterpreted the key on the Natural History Museum guide to Shield and Leather Bugs, which is the one I rely on for these insects. Probably the former! In either case it was an act of sloppiness - probably as the result of a mind that all too often feels it needs to be somewhere other than where it is at present - and I have amended the caption on my previous piece accordingly!