Crompton Life-Light 60w lamp with N.C.B.L.L. stamp

Nothing seems unusual about this lamp apart from its etch (and 250v rating implying it is a "long life" lamp), suggesting it was custom-made for a particular organisation. Such types of lamps were often ordered for use on transport networks and government buildings. Could the "NCB" stand for the National Coal Board? (Edit: indeed it does, and this lamp was of a special 2000 hour variety developed for them by Crompton.)