If the pink growths are hairy, its mostly likely Acer Gall Mite - doesn't kill the tree, and there's no treatment available, but you can pick off badly affected leaves.

Thanks Bamboo I've put Acer Gall Mite into google and it doesn't look like that. It is more of an all over covering that only appears on the underside. Any more suggestions?

Acer Gall Mite sometimes appears as black speckling all over the top of the leaf, and sometimes as either greyish black or pinkish red growths which, when looked at with a magnifying glass, are composed of furry/hairy strands. You picture isn't detailed enough to see closely - nothing else springs to mind.