Is this normal?

I have a plum tree in the garden however it has got bright yellow spots on the leaves. Is this normal or does something need to be done?

 

If there are dark brown spots on the underside of the leaves as well, then it is probably Plum Rust. Usually not a major problem.

 

Nope Its Yellow on both sides if memory serves correct

 

That looks like Plum rust to me.
Normally it is not a problem unless it defoliates the tree on a regular basis. So collect up any fallen leaves and give the tree a good wash down in Winter with a Winter wash. Then before the flowers open and with new leaves just showing spray with Rose clear fungicide. Oh and hope for a less damp Summer next year. This one has been dreadful for all fungus/rust attacks.