HELP!!!

Over the last couple of weeks this tree/shrub has deteriorated badly.  The leaves have started to curl and die.  Normally it's such a prolific grower that it's trimmed twice a year.  The tall pic, top left shows it 9 months ago.  I've no idea what sort of tree it is or where it came from.  The site was an old cottage garden 50 years ago.

Has anyone got any ideas what is wrong and what to do about it please?