As a young ATCA in early 80's at LATCC I certainly saw what the US call a ground stop for DTY traffic North or South bound traffic, did this result in a BA SHT doing that I don't know but if DTY South bound was mega busy it was probably due to early morning heavy North Atlantic westbound flow which would mean BRS/STU being quiet and in them days rerouting traffic could be done by throwing a strip to adjacent sector so who knows?? DTY sector also had a major airspace change during this time to stop over loads as well?