In 1985, the whistleblower Cathy Massiter reported that in the early 1980s, MI5 had a spy, Harry Newton, in the Campaign for Nuclear Disarmament’s headquarters. It now turns out that the police also had their own spy, John Kerry, in the same office (CND calls for answers from inquiry over 1980s police infiltration, 12 September). Did they spy on each other? And was there perhaps a special branch agent keeping a file on both of them?

Rather more seriously, the latest revelation is further confirmation of the state surveillance that many of us at the time assumed was going on, and which was subsequently admitted by MI5 itself (see its official history by Christopher Andrew, published in 2009). The Mitting inquiry into undercover policing is a welcome further exposure of some of the nuts and bolts of such state spying.

The key question, though, is whether it has made any difference. Or does state surveillance of legal, peaceful activities that challenge the status quo continue unabated?
Julian Harber
Former member, CND national council, and former chair, European Nuclear Disarmament

• Have an opinion on anything you’ve read in the Guardian today? Please email us your letter and it will be considered for publication.