I say this is a Stoat, not a Pine Marten. Martens have longer faces, yellow not white bibs, fluffy tails from the root and not black-tipped like this Stoat. You can google and compare photos of the two species to see the differences.
Better exposure would have made the photos more relevant.
I think you are correct about pine marten. Stoats have white bellies not bibs and from the size of the tree ? about a foot wide I guess ,it is too big for a stoat. The "black tip" could possibly be a shadow from the broken branch.