The last line in the article in "Flight Safety" May-June (page 4) 2012 states:-
"The changes are expected to come into effect on the AIRAC effective date 28 June 2012."
The last amendment to AIP, no 71 dated 28/6/2012 has the changes in section ENR 1.4-7, heading "Broadcast Areas", 3.3, subsections 3.3.1 and 3.3.2., but adds an additional upper limit in 3.3.2:-
c) Surface to a nominated level.
(Presumably this covers the eventuality that a control zone overlies the NTA but does not come down to SFC.)
3.3.3 states "The lateral and vertical boundaries are defined in AIP MAP.