For holding a sign outside a courthouse reminding jurors of their right to acquit defendants, a retiree faces up to two years in prison. For hanging a banner reading “Just Stop Oil” off a bridge, an engineer got a three-year prison sentence. Just for walking slowly down the street, scores of people have been arrested.

They are among hundreds of environmental activists arrested for peaceful demonstrations in the U.K., where tough new laws restrict the right to protest.

The Conservative government says the laws prevent extremist activists from hurting the economy and disrupting daily life. Critics say civil rights are being eroded without enough scrutiny from lawmakers or protection by the courts. They say the sweeping arrests of peaceful demonstrators, along with government officials labeling environmental activists extremists, mark a worrying departure for a liberal democracy.

“Legitimate protest is part of what makes any country a safe and civilized place to live,” said Jonathon Porritt, an ecologist and former director of Friends of the Earth, who joined a vigil outside London’s Central Criminal Court to protest the treatment of demonstrators.

“The government has made its intent very clear, which is basically to suppress what is legitimate, lawful protest and to use every conceivable mechanism at their disposal to do that.”

Britain is one of the world’s oldest democracies, home of the Magna Carta, a centuries-old Parliament and an independent judiciary. That democratic system is underpinned by an “unwritten constitution” — a set of laws, rules, conventions and judicial decisions accumulated over hundreds of years.

The effect of that patchwork is “we rely on self-restraint by governments,” said Andrew Blick, author of “Democratic Turbulence in the United Kingdom” and a political scientist at King’s College London. “You hope the people in power are going to behave themselves.”

But what if they don’t? During three turbulent and scandal-tarnished years in office, Boris Johnson pushed prime ministerial power to the limits. More recently, Prime Minister Rishi Sunak has asked Parliament to overrule the U.K. Supreme Court, which blocked a plan to send asylum-seekers to Rwanda.

Such actions have piled pressure on Britain’s democratic foundations. Critics say cracks have appeared.

As former Conservative justice minister David Lidington put it: “The ‘good chap’ theory of checks and balances has now been tested to destruction.”