As the judge in Alexei Navalny’s hearing read out her verdict, sending him to a prison colony for more than two and a half years, the anti-corruption investigator and opposition activist mouthed a message to his wife: “Don’t be afraid. Everything will be OK.”

But as he was led out of the courtroom, it was clear his punishment marked a watershed moment in president Vladimir Putin’s bid to silence opposition figures, and a new chapter in the Kremlin’s use of Russia’s judicial system to stymie dissent.

“They try to shut people up with these show trials. Lock up this one to scare millions more. One person takes to the streets and they lock up another five people to scare 15 million more,” Mr Navalny said in a fierce 15-minute speech before he was sentenced.

Mr Navalny is the most prominent Kremlin critic to be imprisoned since oil magnate Mikhail Khodorkovsky, once Russia’s richest man, was arrested in 2003 on charges widely seen as retribution for dabbling in politics.

The Khodorkovsky trial was a turning point in Mr Putin’s first presidential term, abruptly ending a period where he flirted heavily with the west — even lending support to the US invasion of Afghanistan after 9/11. It marked the start of a campaign against Russia’s oligarchs who were forced to display their fealty or have their wealth sold off to more pliant tycoons.

After the jailing of Mr Khodorkovsky Russia entered a period of “managed democracy” under which the Kremlin brought opposition parties and most of the media to heel.

But Mr Navalny’s jail sentence reveals a Kremlin in no mood to brook any dissent at all. Police have arrested more than 10,000 people at rallies in Mr Navalny’s support since he returned to Russia last month from a German hospital where he had been treated after being poisoned.

“[The Kremlin] wants to send a message and the system must produce that message,” said a senior European diplomat in Moscow. “The verdict was the only verdict allowed.”

So many protesters have been processed in Moscow’s detention centres over the past 10 days that those unlucky enough to be hauled in at the end of recent rallies have found themselves held in police trucks in -11C weather for days at a time.

Hundreds may face charges under a repressive slate of new laws that all but outlaw spontaneous protest, criminalise obstructing traffic, and could be used to block YouTube, the site where Mr Navalny has built his base.

“The current situation is just the beginning,” Tatiana Stanovaya, founder of R. Politik, a Russia-focused political think-tank, wrote on Telegram. “A flywheel has been set in motion, which pits the most powerful repressive inertia against any manifestation of “out-of-systemism” — this will affect activists, journalists, bloggers, media, NGOs, as well as bystanders, witnesses, students and teachers.”

The clampdown shows how the stakes have risen since Mr Navalny came to prominence during protests against Mr Putin’s return to power in 2011. Then, the authorities appeared noticeably reluctant to jail him.

A protest of a few thousand close to the Kremlin in central Moscow in 2013 was sufficient to see Mr Navalny released on appeal a day after a court convicted him of fraud. A year later, the courts spared Mr Navalny prison time but jailed his younger brother Oleg for three-and-a-half years; Mr Navalny likened the move to “hostage-taking".

The Kremlin acted as if Mr Navalny was a minor irritant: he served 13 short prison stints for protests against Mr Putin, but avoided longer jail time.

Gradually, however, the activist became too big to ignore. During a quixotic run for president in 2017, he set up offices across the country and held American-style campaign rallies, even though he knew he had no chance of making the ballot. The point, Mr Navalny later said, was to show Russians another type of young, web-savvy, independent politics was possible.

Conversations with ordinary Russians across the country convinced him he could tap into growing anger at corruption, falling living standards and injustice. A day after his arrest in January he released a video alleging oligarchs spent billions on a lavish Black Sea palace for Mr Putin, complete with a casino, ice hockey rink, and “aqua disco.” It racked up more than 100m views on YouTube.

“We have tens of millions of people living without the slightest prospects for the future,” Mr Navalny said at his hearing. “And they’re all silent. They try to shut people up with these show trials.”

The Kremlin’s draconian treatment of Mr Navalny may partly stem from fear of that anger as Mr Putin’s approval ratings skirt record lows. But it may also indicate that, in Mr Putin’s eyes, Mr Navalny somehow crossed the line from opponent to traitor and should be dealt with appropriately.

After Mr Navalny helped expose a hit squad from the FSB — the agency Mr Putin once chaired — and tricked one of them into admitting his role in the poisoning, the Kremlin angrily declared he was a US agent.

Margarita Simonyan, editor of Kremlin propaganda network RT, said that the move to jail Mr Navalny was a response to “what western secret services and the so-called civilised world are trying to do to Russia” by overthrowing its government.

“No objective, right-minded person could fail to realise that Navalny is an instrument of this huge machine that is grinding up the whole world, chewing up countries and states, without ever choking on them,” she said on an RT broadcast. “This toolkit has been running wild for too long.”

But despite the threats, Mr Navalny chose to return to Russia and rally his supporters.

“I want to say that there are many good things in Russia now. The very best are the people who aren’t afraid — people who don’t look the other way, who will never hand our country over to the officials who want to trade it for palaces and aqua discos,” he said.