Plums trees, mummified fruit, poor yields

[Chockabloke]

A friend of mine has a plum tree that was quite prolific last year, this year it had lots of fruits starting to grow but all of a sudden the fruit have started to go off and starting to mummify. Unfortunately I don't know what variety it is. In my Hessayon fruit epert the closest description I see is brown rot, due to the mummified appearance of the fruit. However, there doesn't seem to be any rot as such, just a mummified look about it. There doesn't appear to be any signs of problems on the leaves. Can anyone help?

I also have a plum tree (again i don't know which variety it is) which is about 8 ft high that doesn't seem to have many fruit on at all. Again the leaves and branches look healthy. Could this be due to not being pruned correctly last year?

Thanks in advance