Somebody has written about it, but I do not remember the keywords that would retrieve the thread... it has definitely been mentioned, and more than once. Since you are in London and not in the middle of nowhere (an American expression but you get the gist anyway), why have you not told you physician about it? The primary care physician or whatever the name for the main doctor through the NHS should at least know about the problem - if he or she cannot address it, they will refer you and maybe do some tests. Painful and overly long erections are a medical concern.