I transferred in 1990 - there was no residency requirement then.I was in DNR/OES1 from 1981 - 83. Five year residency was the rule then, as I used to respond to letters from aspiring Commonwealth candidates, many of whom would have been snapped up if we had been given the chance. Lots of keen young Saffers, Kiwis and Aussie guys and gals.
If you're referring to a DCI that was implemented in 2013 well hey, sh1t, bully for you sport - I left MoD in July 2012 and retired the following year.
But the 5 year residency requirement was, from, my personal experience, the norm thirty years ago and bugger all to do with the EU.