> If a person without a warrant gets off the tube and walks in a general direction of a protest, I wouldn't see any grounds for arrest.

The police don't manage mass protests this way either. If they want to stop you joining a disruptive protest they just cordon off streets, close tube exits, stand in the way and tell you to turn back.

But severely disruptive micro-protests are now a significant problem in London; I am quite relaxed about the idea that someone known to be planning to seriously disrupt might get tracked to their destination, and I suspect so are they, or they aren't very serious about it.

I think people from the USA really misunderstand how policing works here. When we say we are "policed by consent" it is taken pretty seriously.

Back when I was a student, this idea of facial recognition was only a glimmer of possibility and the idea of all of this would have got my freedom fighter hackles up.

But if you've ever been in a tube station, one of the deep lines, when they've had to close exits and you're one of thousands of people who need to get out, you realise that these are high-pressure environments where even British reserve and fairness begin to fray. They are very vulnerable places. So I look at this plan and I am like… nope, doesn't bother me. Getting in and getting out at rush hour bothers me.

I am not without my concerns about the mobile recognition vans; I think there is a risk that they have a chilling effect on gatherings that is disproportionate. I dislike that concept in much the same way that I dislike our regional police force's tendency to get the helicopter out when a bit more road policing might do the job.

But inside the tube? Nope, facial recognition seems like a pretty worthwhile tool, not least because it could be so efficiently deployed.