>> They're doing that up on the Moors this year, <<

I've seen a variety of interesting news about restoring the much-ravaged parts of the Isles. Some will take years of work to achieve, like restoring megafauna wiped out by humans. But some can be done by expanding the range of animals (e.g. water voles, beavers) and trees (e.g. willows, oaks) that have survived.

>>I might just put in a few days of volunteer work if I'm able, although it's hard graft on the old back.<<

Find an organization near you and talk to them. Remember that not everyone has to do the same job on a project to contribute. Bushwhacking is brutal on tools. Can you sharpen an edge and replace a hinge bolt? Jerryrig something on the spot? Because I'm betting most groups won't have a blacksmith available to fix what breaks, which would make you more valuable than another bushwhacker.