It was prohibited during the days of intensive IRA activity, when we were all deemed 'targets' of those terrorists. We employed a wide range of measures to protect ourselves, including not using mail forms of address showing our rank, checking under vehicles for IEDs, varying routes to/from work. They were 'interesting times' - I was only 'bombed' twice in UK, and lost a good buddy murdered on his doorstep in Germany.
Things were relaxed after the 'peace talks' which placed former IRA leaders in Government in Northern Ireland. It still felt un-natural wearing uniform in public after so many years of prohibition.