What's the thickness of the metal? It almost looks like it could be an arm from a set of tongs that would be use to pick up ice blocks or move large stones around.
Since you've found a number of them at different locations, i think it might be a slate repair hook, used to replace broken or slipped roof slates as a simpler and less unsightly alternative to lead strapping. At their simplest, they’re just a piece of copper that’s thin enough to fit between the existing tiles, with a spike at one end to nail them into the roof timbers and a hook at the other end to wrap round the bottom of the slate being replaced. Like this, but older ones for heavier tiles may be substantially more robust.