No interactions present.
How about a few more clues Mike! Size, hostplant? Did it move? All I can suggest is that it might be the larval case of the micromoth Coleophora palliatella. This is an oak feeder but apparently does sometimes move its case onto other plants when it is ready to pupate.
Entomologist and biological recorder
Well, you know Martin I don't want to make it too easy for you. But seriously I'm sure I did write some more details but they seem to have vanished, actually not the first time this kind of thing has happened.
I would guess it was about 5mm very approximately and its on a bluebell leaf i think (this is a section of the original picture in which it suggests more strongly bluebell or similar linear leaf). wood does have oak and bluebell but also a wide range of other trees.
Lat/Lng: 51.955707, -0.656901
OS grid ref: SP923294