I only heard of CND activity at Coventry Group HQ. Durham HQ was in the city centre, beside the river and next to the ice rink, and had a high chain link fence and to the best of my knowledge wasn't targeted.I can believe that, going by some of the anti-nuclear people that I spoke to back in the 80s. They didn´t have a clue, and wouldn´t even try to listen to an alternative viewpoint.
They would have seen an ROC post as part of the fascist military establishment. The fact that it had something to do with radiation monitoring would have enraged them even more.
Coventry Group HQ on the other hand was actually at Lawford Heath near Rugby, and was on a quite large and open site - we even had a Hawker Hunter as a gate guard. The only attack that I'm aware of involved some CND types entering the site (breaking in would be an exaggeration) and painting "ROC MEANS DEATH" on the road. Bless.
I was informed that Durham Group had had some CND members join up who had been passing on details of exercises to their friends. However what happened to our Kim Philby walts, I have no idea. Anyway, nothing that we did was really secret. We put on a display for the general public at Durham Castle, including lots of documents marked "Restricted" in 1989 or 1990. I think that the only people who turned up were members of the Corps.