My Old Bramley Apple Tree has tilted, should I prune it or leave it as it always produces hundreds of apples and why has this done it?

Old Bramley trees are prone to this. Don't prune it unless you really feel you must. Make a crutch for it. They're usually made from a piece of 3 x 2 with a deep notch cut into the top, and the right length to wedge under a strong lower branch. You will have to keep adjusting it gradually until the tree is upright again. You can also use a strong, forked tree branch, cut to suit, if you want the rustic look.

I agree with BBB, as regards to the props needed to hold your tree up and prevent it leaning over further. The main reason for your tree doing it is because the root stocks are brittle and break in later life.

Thank you for your help my son is busy sorting out a prop