More than a thousand political and campaigning groups have been targeted by undercover police operations over the years since 1968.
In the latest instalment of a slowly-accumulating mass of revelations, the Guardian on 15 October published a list, compiled by the Undercover Research Group, of 124 groups within which police agents were placed between 1970 and 2007.
The undercover cops quite often enticed activists (generally women) into sexual relationships, and even had children with them. The list also records claims that in some cases the cops acted as provocateurs, making the groups vulnerable by leveraging them into risky or illegal activities.
Almost all the groups targeted were broadly left-wing: the list records only three cases of far-right groups being targeted.
Some 16 campaigns against particular police abuses were targeted. Such campaigns are unlikely to consider illegal activity, and it looks as if they were targeted to get the police information and material to fend off abuse claims.
An official Undercover Policing Inquiry has been grinding on slowly since being declared in 2014 and started in 2015 - as a response to a series of exposes starting with the Mark Kennedy affair in 2010.
Since March this year victims of the police operations, after increasing frustration with the official Inquiry, have been seeking to bring a legal case against the Government to make it appoint a diverse panel for the Inquiry rather than it being run by a single judge.