Bug on a gate

This shield-shaped beetle thing was on my gate this afternoon; I've often seen bright green ones this shape, but not this rather less appealing brown job. I've been poring over pictures of stink bugs, which seem at the moment to be elsewhere - like the US - and brown soldier bugs, which are less harmful to crops, apparently. However, I can't be sure without going back out to look for a creature that though interesting is about the size of my finger-nail (it would help to see if it has white bits on its abdomen, you see) and even were it to have remained on the gate after the sun went and night fell, the thought of actually bug-hunting in the dark appalls me, frankly.

So it's over to my erudite friends on Blipfoto: what is this? Is it A Bad Thing, or merely an interesting subject for a blip on a quiet afternoon?