From time to time I see references (and eBay auctions) for the Manifoil Mark IV combination lock, commonly used on UK government containers. Were there ever any Manifoils that were not Mark IV?

Is there any sort of history for it, such as when it was introduced, and how secure it claims to be (as opposed to how secure it really is)? I gather it is/was used on filing cabinets and the like but not necessarily on serious safes.

Also, it appears that it is no longer made. See for example Locksmith Hoddesdon - Locksmith Blog which shows a modern replacement. The dial looks very much like a Sargent and Greenleaf, but the lock body is not something I've seen before. Any information on this replacement, such as who makes it?