The "Procession" Rule
If you are moving from Point A to Point B, that is a procession. You must give the police 6 days' written notice (unless it's not reasonably practicable, i.e., an immediate response to a spontaneous event).
Tip: If you verify your route beforehand and stick to it, the police have fewer grounds to intervene under Section 12 of the Public Order Act.
Dealing with Police
"No comment" is not just for criminals; it is for your protection. If stopped, ask "Am I being detained?" If no, walk away. If yes, ask "Under what power?". Film everything.
Safety in Numbers
Use the Buddy System. Never attend a protest alone. Have a designated meeting point if active comms go down or if the crowd is dispersed. Write a lawyer's number on your arm.