Okay, this is a bit long winded but I want to make a point about using local forces as an anti-terrorist organisation, so bear with me.
The UDR wasn't the smartest move the Brits ever made but it was better than leaving the defence of the state to the RUC which had to be overseen by regular British infantry units, the RUC were simply unable to effectively manage terrorist activities. It was initially thought that an organised and well trained territorial infantry regiment (UDR) would be effective and could even be a way forward for uniting both Catholics and Protestants against the IRA but as it turned out the vast majority of recruits to the UDR were Protestant. What Britain effectively managed to do was create an organised Protestant infantry regiment, they were trained in basic counter terrorist techniques but in my personal opinion they were ineffective and never really stood a chance.
The UDR primarily manned checkpoints and provided security at key locations but the real problem was that a lot of classified information on things like the UDR strength, training, position of check points, equipment etc was continuously fed back to both the IRA and the Protestant volunteer forces. There were also a few occasions when UDR weapons and ammunition miraculously disappeared only to find its way into the hands of either the IRA or mostly into the hands of the Protestant UVF paramilitary forces, the result was that more UDR men were killed off duty than in regular service, which in turn escalated the situation.
The ultimate role of the UDR was to help free up regular British regiments from regular tours of N.Ireland but it didn't really work out. Brit regular forces were still required to support/oversee the role of the UDR.
In short, the answer is that N. Ireland was a drain on British regular forces at a time when those forces could have been better deployed elsewhere, it was a real problem considering that this was happening during the period of the Cold War. I think its also fair to say that had Britain been able to focus solely on the Irish problem then we would have had more than enough troops but given that regular forces were required elsewhere there was never going to be enough regular troops to fight insurgents.
In my humble opinion, one of the key problems in raising a territorial or militia force from the local population is that there are no cast iron guarantees that the very men being armed and trained are not insurgents themselves, it happened in Vietnam, Ireland, Iraq and Spain, in fact any country that looks to employ civilians from a divided nation runs the risk of arming and training those that they wish to defeat. In all honesty, the only time that I have ever read about an effective militia or auxiliary force was way back with the Roman occupying forces. they understood that local men could not be relied upon to fight against their own people, the result was overseas posting and foreign auxiliary forces being used to police or defend captured territories, those foreign regiments/legions had no emotional or patriotic ties to the occupied country in which they served so they were successful.
So I'll end with a question.
Isn't a militia nothing more than a State/government approved guerrilla force, and why does everyone react negatively when these forces break the rules, if you arm,train and then let lose a militia with an axe to grind then be prepared for the consequences. For me personally a militia or territorial force can cause more headaches than anything else. I know there's that old saying of
'fight fire with fire' but I can't think of any home grown unit that has been successful in counter insurgency. Just about every unit that I have read about from the Civil War had issues aka Moccasin Rangers, Mosby, Quantrill etc, in fact we still see similar problems with local forces in places like Iraq and Afghanistan.
I'm here to learn so I won't be offended if you don't agree with me, fire away.