Through various ATC sources, I do believe there have been a few scenarios based upon Icelandic eruptions practiced over recent years at SCATCC/Shanwick, each one getting larger in scope. Long overdue eruption anticipated, though don't know if it's the peak you quote BOAC that is the main problem. Scenarios range from minor diversions, through oceanic turn-back a la 9/11, to full closure of UK/Oceanic Airspace. I believe, that is; I may be wrong.
Maybe others more qualified and knowledgeable than I could comment.