Excellent piece by Simon Jenkins in today’s Guardian – https://www.theguardian.com/commentisfree/2017/oct/18/mi5-lost-plot-britain-safer-than-ever-andrew-parker-terror.

It really is important to distinguish between politically-motivated crimes that ‘only’ hurt people, and politically-motivated crimes that genuinely threaten the state – or democracy, or the British way of life, or whatever. Terrorists want to have their actions put in the latter category. That’s their whole purpose – to bring about political or religious change, through ‘terrorising’ the general population. Parker’s scaremongering must be music to their ears.

They understood the difference in the late nineteenth century. See my The Origins of the Vigilant State (1987).