Posted: 17/04/2014 at 15:20
Thanks for the responses.
Verdum - it's definitely not waterlogged. I'm on the east coast of Scotland and we really haven't had a wet winter at all. The leaves were like this all of last summer.
BusyBee - I fed it a lot last summer, but it didn't seem to make any difference. Will try again and see if it makes any difference.