After talks between the group running the vigil, Reclaim These Streets, and the police proved fruitless, the organizers went to the courts to try to win permission for the event.

When the High Court declined to intervene, Reclaim These Streets canceled the gathering. Nonetheless, crowds arrived at the park throughout the day, with visitors including Prince William’s wife, the Duchess of Cambridge, who was among many to lay flowers at a makeshift tribute around a bandstand.

A turning point appeared to come when people started to make speeches, prompting the police to move in and break up the gathering. Presumably, this was because the event was turning from a vigil, which the police seemed willing to tolerate, to a demonstration, which they were not.

Adam Wagner, a human rights lawyer who advised Reclaim These Streets, said, “The police created the situation that allowed it to become an unruly disorganized mess, and then felt they had to carry out enforcement.” He added that in failing to reach an agreement with the group to cooperate in organizing the event and in that way manage those who wanted to attend the vigil, the opportunity was lost to exclude others, such as anti-lockdown protesters.

In a statement on Tuesday, Reclaim These Streets said it had lost confidence in Ms. Dick, the Metropolitan Police Commissioner, who the group said had granted them a meeting on Monday of just 15 minutes. “We pressed the commissioner for a clear answer on what an acceptable form of vigil would be under the legislation and she failed to provide an answer,” the statement noted, adding that the actions of the police “were putting the safety of women exercising their right to protest at risk.”

With no written constitution, rights to protest rely in Britain on a general human rights law and on an obligation on the police to use force proportionately. But critics of the coronavirus rules note that the speed with which the regulations were passed through Parliament has left a legal jumble.

Pippa Woodrow, another lawyer advising Reclaim These Streets, said, “A lack of clarity has been a real issue from the outset, and that might have been understandable at the beginning but we are now a year into this and our laws are still no better.” Having stopped some protests, the police seemed to feel that they would have looked inconsistent if they had let this vigil go ahead, she added.