Q.Pruning
I have a damson tree that produces loads of fruit but is in desperate need of pruning, when is the best time to do this and how much should I take off? It is too tall to be able pick the fruit from the top now even with a ladder so would like to make it spread side ways rather than continue going up.

These links will help you.
https://www.gardeningknowhow.com/edible/fruits/plum/growing-damson-plum-trees.htm
https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-pruning.htm