>The Republicans weren’t as heavily infiltrated by British intelligence, Unionist communities were far more compliant with the RUC, and the Republicans tended to use the border as a means of escaping the RUC in safe houses in the South. Maybe that’s what you meant by ‘effective’
The British Army's [assessment(]http://news.bbc.co.uk/1/hi/northern_ireland/6276416.stm) of the IRA was' a professional, dedicated, highly skilled and resilient force' while their opinion on loyalist paramilitaries and other republican groups are described as "little more than a collection of gangsters". From the British Army's analysis of Operation Banner, the 'IRA developed efficient intelligence, quartermaster, finance and engineering branches.' The same document assessed the two main loyalist protagonists as 'heavily involved in racketeering, extortion and other forms of serious crime. The following sentence is also relevant; 'The loyalist movement rarely attacked the security forces. It did so on occasion in response to political activities that were unpopular with the protestant community' A. R. Oppenheimer published a book last year IRA, The Bombs and the Bullets: A History of Deadly Ingenuity, His opinion was the IRA was 'most adept and experienced insurgency group the world has ever seen through their bombing expertise'. Here is a brief interview with him So to attribute the effectiveness of the IRA to the border and unionist compliance is both anorexic and inaccurate. The border was a factor but only a factor.
Again the HMIC found that the HET pursued cases involving State actors with less vigour than non state actors. Investigators from the HET lost their jobs and had their homes raided over their conduct. Again I will cite the activities and role of Robin Jackson and I will add this report from the police ombudsman that found for a 'number of years police acted in such a way as to protect informants from being fully accountable to the law.' And again John Weir was found credible by the Gardai and the Barron inquiry I don't think there is actual crime of collusion in British law. The use of the word is misleading. If you want to claim that it requires a 'smoking gun' to prove collusion I would say that this is an exercise akin to catching smoke in a bottle. Instead lets look at collusion as term to describe occasions where State forces both actively and passively co-operated with non state actors. Passive collusion is a simple as not doing their job, not following leads. not collecting evidence, losing evidence. Active collusion would mean taking a more active role, like providing intelligence and material. I will cite another two instances where the conduct of state forces was questionable, those are the cases of Robert Hamill and that of Loughinisland.
So in recap, there are several documented instances of 'collusion' in the history of the conflict. Occam's razor can be applied in a single case, but when the same questionable conduct appears repeatedly, I don't think it's unfair to say that the belief that there was repeated collusion in many forms both active and passive is without foundation.