Posted: 16/09/2014 at 11:37
Sorry that it took me so long to reply to you, but we have been on vacation for a couple of weeks. We only returned last weekend and there were some matters that needed handling first.
Now, about Stemphylium vescarium, I have found this document for you: https://secure.fera.defra.gov.uk/phiw/riskRegister/viewPestRisks.cfm?cslref=23258
I couldn't find anything written by the RHS, but if you google on Stemphylium vescarium, there are other documents to be found, although not necessarily about the situation in the UK. But maybe you could ask about it at the government department that published the document?
Okay, now let's go into the matter of the "dead" bark and cutting through barriers. In the Netherlands it indeed used to be common practice to take a piece of bark away (not always dead bark) and judge the tree's situation. But over the years, experts have come to the conclusion that this practice more often than not damages the tree more than the wound does.
After intensive experiments at Wageningen University (among others), it became quite clear that, given the time, trees are very capable of healing themselves by overgrowing wounds, which is explained by the C.O.D.I.T.-principle. There's a lot of documentation to be found about that principle, but this one explains it in simple words: http://en.wikipedia.org/wiki/Compartmentalization_of_decay_in_trees
We do cut off small branches as some diseases can be identified by discolorations within the tree.
I think you might be able to learn more if you contact a European Tree Worker. More and more people are learning what magnificent creatures trees actually are, what they mean to our environment and how to take care of them, but we're still a long way from understanding Mother Nature.
Kind regards, Flowerchild
(BTW, sorry for the long post)