From what I can see from the pictures, it looks like the pear leaf spot fungus (Mycosphaerella pyri).

Sorry Myron, I don't agree, it looks much more like Pear Leaf Blister Mite. Unfortunately, there is no treatment available for this other than picking off affected leaves, but if the infection is extensive, then you can't really remove all the leaves. It does not affect the fruiting ability of the tree, so its a little pest that has to be tolerated. Its caused by a microscopic gall mite known by the unlovely name of Eriophyes pyri...

No problem Bamboo, it's good to get a second opinion from someone and you're probably right. I also first thought that it could be blister mite but discounted it as all the blister mite damage that I have come across seemed to be brown and patchy. Maybe this was the secondary stage causing parts of the leaf structure to die?

Yea, it does that, you end up with black parts in the leaf. The only thing that's slightly worrying is that the same yellow discoloration is present on those fruitlets... I hope its not viral...

Thanks for your replies. I'm still not sure what the best course of action is though

If its blister mite, there is no course of action you can take - google both conditions (Pear Blister mite and Pear Leaf Spot) look at the images for both and compare with your tree. You can use a suitable fungicide for Pear Leaf Spot, but not for Blister Mite.