Oxfordshire, United Kingdom

What is wrong with this Bramley Apple tree? I first noticed bark coming off a branch several years ago, and I suppose I really should have done something about it then. I probably should have treated the branch with something or cut it off, but in winter it is cold outside, and this makes me forget about pruning/cutting back trees. It gave a huge yield last autumn.
I went out to look at it last week, and then noticed that the trouble seems to have spread to more of the tree. The first photo gives an idea of the size - it is obviously mature and well-established, and it was like this when we moved here years ago. You can see a piece of bark hanging from the branch in the middle - this is where the trouble began.
The second photo is taken from up a ladder, and shows the typical garden shed next to the tree, and the beech hedge which is about 7 feet high; this gives an idea of the scale. The third photo gives a closer view of the foremost main branch where the really noticeable trouble is.
I seem unable to send more than three photos with this Question, and so I will send three more with another Question which I will entitle 3 More Photos of Bramley Apple Tree Trouble.
The fourth photo will give a closer view still, and the fifth and sixth will show close-ups of the other two main branches, which now seem to be different from before.

• 1 Mar, 2014