Russell T. Davies, the potentate behind 'Doctor Who', 'Torchwood', and 'The Sarah Jane Adventures' has said that the acronym of UNIT no longer stands for "United Nations Intelligence Taskforce". Which is just as well since the United Nations took umbrage at the use of their name, just as they did when it came to what U.N.C.L.E. really stood for. (Just for the record, it's United Network Command for Law and Enforcement.)
But that's not to say that it wasn't the United Nations Intelligence Taskforce originally in Toobworld. It could be that there was a restructuring of the taskforce during the tenure of Kofi Annan as Secretary-General. So UNIT was now able to stand on its own without being tied to the capricious whims of the member states in the United Nations.
And I still believe Thomas R. Sloane III was an agent for that same version of UNIT in 'A Man Called Sloane'....