I reckon it's been left there as a prank to see how long some well-meaning person will attempt to return it to its rightful owner. I'd just get it in the tackle bag if I were you. Or send it to the National Museum of Vintage Caving Equipment (aka Mark Wright) to see if they can work out whether it's pre or post-war at least
The red & blue item looks similar to the chest harness that Dragon caving used to make. It was the most comfortable chest harness I've ever had. Depends a lot on your shape/size though!
I can modify it and use it for something myself if necessary. If you look at the picture the front strap is completely knackered anyway. But before I transmogrify it into a new life, I wanted the owner to have every opportunity to claim it back.
I'll leave it until the end of the week then decide what to do with it.
Nowt wrong with caver post phhole - our fellow cavers provide a wonderful service (I do it too) and besides, I enjoy the challenge of sorting the logistics.