I would imagine the police Commanders decision log would look something like this:-
1) have facilitated protest for nearly 12 hours now/ need to balance rights of protestors with rights of others. Protestors have no right to occupy highway indefintely
2) Darkness is approaching making public order policing inherently more difficult/dangerous
3) Have not got resources to police crowd through the night via kettle or cordon. Public order officers deployed since early morning need relief
4) FIT intel
Decision:- clear the street
1) have facilitated protest for nearly 12 hours now/ need to balance rights of protestors with rights of others. Protestors have no right to occupy highway indefintely
2) Darkness is approaching making public order policing inherently more difficult/dangerous
3) Have not got resources to police crowd through the night via kettle or cordon. Public order officers deployed since early morning need relief
4) FIT intel
Decision:- clear the street