These certainly look like fungal diseases. There is usually no cure for such diseases. If I may offer some advice..

Remove carefully infected leaves/branches and burn them. This will kill the infected parts and kill most of the fungal spores to help reduce it spreading..

I'll pm you an email address of  a work colleagus who is a fungal expert in the Food and Environment Research Agency (FERA) Plant Health clinic (part of DEFRA). I don't know if they will help as they run a commercial diagnosis clinic for this sort of thing and it is notoriously difficult to make a proper diagnosis from a picture since many symptoms for different diseases look so similar.

Pm coming up.....