Posted: 14/06/2013 at 23:45
Hi Nicola ... emailed various organisations for help diagnosing my birch tree's problems and had a very prompt reply from the Plant Health Department at Forestry Commission Scotland - from the photos I sent them they are pretty sure the culprit is as follows ...
"The leaf spotting on the second photo is almost certainly caused by the fungus Marssonina betulae which in a wet summer can cause heavy defoliation and sometimes shoot die back. With large trees there is no practical control of this fungus and although the fungus may cause shoot die back it should not kill the tree although the foliage may be more sparse this year."
Sure enough, Googling the fungus name led me to images which do match my tree's symptoms. Will wait, with interest, to see what the other organisations have to offer, and will post here if there are different views.
Still apprehensive about the long term survival of my Very Old Lady of the Woods if we get more wet summers - leading to more fungus, more die back, and less leaf cover weakening the tree ..... but your 30 year old youngster should be OK!