Jonathan Sumption accused ministers of “humbug” in trying to pin responsibility on the police – arguing the Met was placed in “an impossible situation”.
Both Boris Johnson and the home secretary have criticised the scenes on Saturday, when officers grabbed women, forced them to the ground and led them away in handcuffs.
But Lord Sumption said: “The problem lies in the framing of the regulations – and this was a deliberate decision made by the home secretary, who objected to demonstrations or protests last year.”
The former judge – a fierce critic of lockdown regulations – questioned whether the “considerable brutality” used by the police on Clapham Common was justified.
However, he said: “The government’s expressions of concern about what happened seem to me to have a large element of humbug, because it is the direct result of a decision made last autumn.”
In the first lockdown, there was “an exception for demonstrations and political protests”, provided rules had been agreed in advance with the police.
“That exception was deliberately removed at the end of last year, because the government did not want to allow political protests,” Lord Sumption told BBC Radio 4.
“Now, of course, the government is mainly concerned about protests against its own policies – but the problem is you can’t have an exception for demonstrations and protests that the government likes, but not covering demonstrations and protests against the government itself.
“And the real problem here is the absolute nature of these regulations which do not contain an exception for perfectly legitimate and peaceful protests.”
In contrast, the German Constitutional Court had ruled that people must be allowed to gather “to make their views about political and other issues felt”, he said.
The criticism came after the prime minister said “people have got to have confidence in the police”, ahead of chairing a meeting of the government’s Crime and Justice Taskforce.
Meanwhile, an ex-police chief warned the public to be “really worried” about a new crackdown on protests – accusing the government of putting rights “fundamental to our democracy” at risk.
The Police, Crime, Sentencing and Court Bill will expand police powers to stamp out protests that cause “serious unease” and create new penalties for people who cause “serious annoyance”.
But Peter Fahy said it was wrong to “rush legislation” just because ministers are angry about the demonstrations staged by Black Lives Matter and Extinction Rebellion last summer.
“We’ve learned one thing this weekend,” the ex-chief constable of Greater Manchester Police.
“It’s the right to protest, the right to gather, the right to have a voice is fundamental to our democracy and particularly British democracy,” he said.
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