Update.
I have today spoken to the NRA (shooting division) and the warning is still in force.
The notice is (or should be) still on the notice boards.

Summary is : The warning came about as a result of 'grave concerns' by both the Police and the Military after both had 'problems' and a number of incidents. (I wasn't aware that the Police were still using 7.62 No4s - Enforcers etc. I thought they'd all be sold off or scrapped)

There is a management meeting this week and this subject is on the agenda.
The results will be published in the Spring edition of the Journal, and, posted on the notice board.

The person I spoke to had no knowledge of any specific incidents, or what specific ammunition the warning referred to.