So this year it's been on its own, and I gave it a bit of a mulch with some lawn clippings because I was too lazy to carry them to the top of the garden.
I now have what may be the world's happiest apple tree. It practically stands there humming to itself and dancing. The tip rot has completely vanished, and it is laden with delicious red apples which are pretty much scab-free. Result!
The apple trees at the top of the garden are not doing quite so well this year, but I think perhaps they are getting a bit congested. This winter I shall chop everything right back all around them and hope to be swamped in a sea of apples next autumn.