UPDATE On inspecting all the other branches, I found one of the branches in the following state. It shows the bark beginning to fall off the tip, explaining how the other branches have developed.I cut it off, sealed it in a box and put it in the fridge whilst I wait for an identification of the problem. It is still unclear what has started it - i suspect some sort of parasite?
This has happened to one of my apple trees over the past few years, I'm now concerned because it is happening to other branches and there is very little one year growth on the tree. This is the shape of the tree, and ringed in red are the branches that are affected. Does anybody have any ideas what might be causing this?
Here's another picture from a different angle, clearly showing the cambium layers and the profile of the edge on them. Nobody else has pruned the tree to our knowledge, could an animal have caused this type of damage? Here's a shot of the same damage having occured to another branch