I'm sure we had this discussion recently in "another place". My view is that two separate things happen when you get an IMC rating on your JAA PPL. One is that you exempt yourself from the clause in your license that says you may not fly out of sight of the surface. The second is that you gain the right to fly IFR in visibility down to zero in anything up to Class B airspace within UK airspace. The second right is not one that the CAA can bestow upon you outside UK airspace.
Oddly I also think that the same cannot be said of a UK CAA PPL and an IMC rating but I can't help but suspect that that is a drafting error in the ANO.