The Islington Gazette published a story this week about businesses in my part of North London joining forces with the police to set up a group to share "urgent police alerts and images of people in the area suspected of being extremists".
On receipt of a WhatsApp message, the senior managers in the group will distribute it to their staff who are expected to "ensure the safety of customers".
It's apparently a one-off scheme backed by the Metropolitan Police, and the participants in the Angel area of Islington include the Royal Bank of Scotland, the Hilton Hotel and Business Design Centre. It's billed as a response to the terror attacks in Paris at the end of last year.
"The idea is to get people looking out, and hopefully this alertness will prevent anything happening," according to the Angel Business Improvement District (BID).
Having been caught up in one of the failed bombings at Warren Street Tube station on 21 July 2007, I know just how frightening even an unsuccessful terror attack can be and I need no lessons in the importance of spreading information speedily and effectively so that people can be kept safe.
And I'm all for using new technology to communicate efficiently. For the police, I can see that WhatsApp may be the best way to get information out to businesses quickly in the event of a serious incident.
However, the idea of designated business bosses sharing images of people they believe are "extremist" raises serious civil liberties issues. In the context of the fear, suspicion and misunderstanding raised for example by the government's Prevent strategy, it's extremely worrying.
The business groups themselves seem alarmingly unaware of the civil liberties implications of their scheme. They say that "only an allocated boss of each member company is allowed to post a warning".
But this implies that if a boss of one of these companies doesn't like the look of someone or thinks they may be an "extremist", they will use social media to spread their concern to all other businesses in the area.
Further, the BID "eventually wants to extend the scheme to smaller businesses and residents' groups". This sounds like encouraging community participation in a scheme to inform on neighbours and fellow residents.
You'd think that too many unsolicited reports from shopkeepers and community groups would strain the police's stretched resources and divert them from more pressing work. It also gives new meaning to the expression "shopping your neighbour".
A police spokesperson quoted in the Gazette admits the possibility that mistakes may be made but offers the reassurance that: "We will deal with that if it ever comes. There are strict protocols. I have spoken to these people, who are in positions of trust, at length. I'm confident it will only be used if something serious happens."
I wish I could be so confident. People hold prejudices, and one person's "acting suspicious" is another's just waiting to meet a friend. In times where "extremist" and "Muslim" are elided in many people's minds, and where "Muslim" seems to mean "any brown person", it's not hard to imagine alerts being triggered simply because of the colour of someone's skin.
Aside from that being horrible on its own terms, it will also exacerbate the very problem it's meant to solve. If we really want to drive people into the arms of the extremists, treating them as suspicious before they've done anything wrong is precisely the way to do it.
Reporting on neighbours has some very ugly precedents in history, and those of us who care about civil liberties and freedom of speech and association should take heed. This apparent democratisation of oppression by WhatsApp should be questioned by everyone participating in the scheme.
Caroline Russell is a Green councillor in the London Borough of Islington and the party's No 2 candidate for the London Assembly