@Turph
You have hit upon the dilemma.
Buffer Zones are rare because they clash with lawful rights to freedom of expression and the right to peaceful assembly. The state is expected to facilitate peaceful protests and to that end:
- the police have to be tolerant of a degree of disruption
-the police have to produce convincing evidence before restricting those rights
- in case law, the authorities insist that it would be unacceptable to restrict where and how the peaceful protesters can assemble.
For instance:
^the right of the defendants to assemble for the purpose of expressing and discussing those views, extends to the manner in which the defendants wish to express their views and to the location where they wish to express and exchange their views.
If it were otherwise, these fundamental human rights would be at risk of emasculation^ " (Hall v Mayor of London, 2010)
It's different when the police anticipate that the assembly isn't going to be peaceful. Where there are threats of violence and a risk of disorder anticipated, then the police have Public Order powers to curtail, restrict and prevent the assembly.
I think this will happen:
There will be a Buffer Zone. Protesters will force the police's hand and get themselves arrested. They will sue the Commissioner under the Human Rights Act. They will win and damages plus legal costs will be awarded.