So let me guess, it's going to deployed at all the tube stations that lead to the event?
So let me guess, facial recognition is going to be deployed at all the tube stations / overground stations that give access to the route of the Notting Hill Carnival, or the stations from which people travel from?
It's still the "Notting Hill v Chelsea Flower Show" question of where to deploy and the MET has 'chosen' Notting Hill every single time for this trial.
A face is a face, if this is a trial. If the MET wants to use intrusive tech, it has to be trialled in all areas, to make all sections of society know how uncomfortable it can feel.
This is supposed to be an event that brings people together, not single them out for vetting 'by association'.