Last Saturday Grigory Mikhnov-Vaitenko, the Archbishop of Russia's Apostolic Orthodox Church, was arrested in St Petersburg on his way to a memorial to victims of Stalinist terror, where he allegedly intended to carry out a Christian memorial service for the newly departed servant of God Alexei Navalny.

Later the same day, an ambulance was called to the police station and took Archbishop Grigory to hospital with a stroke, where he is still believed to be. In the meantime, another clergyman stepped in to hold the planned memorial service, with further arrests along the way.

In total, hundreds of people have been arrested all over Russia in the past few days for honouring Navalny's memory with Christian services or simply by bringing flowers to memorials of victims of communist terror, where the authorities have deployed 24/7 police patrols with orders to identify all those grieving for Navalny. The chain reaction of terror goes on.

Political assassinations have been the trademark feature of the Russian regime throughout Putin's era. Perhaps Mr Putin (having lately acquired the taste to meditate and lecture others about his personal place in history) quietly prides himself for having excelled the great poisoning princes of the Renaissance. Yet, there is one way in which the death of Alexei Navalny stands out in the long line of deaths of Putin's other opponents from Alexander Litvinenko to Boris Nemtsov: there has been no real attempt to cover the tracks.

Navalny had narrowly escaped an infamous attempt to kill him by putting Novichok into his underpants in 2020, and then caught the FSB red-handed in a masterpiece of investigative journalism: Navalny phoned one of the assassins posing as an aide to the FSB boss and tape-recorded the assassin's detailed report on the failure of his mission.

After a scandal like that, Navalny's death in Russian state custody was bound to look extremely suspicious in any event. It was not for nothing that President Biden personally warned Putin in 2021 that Navalny's death in prison would have "devastating consequences".

A few weeks before his death, he was suddenly transported to a remote Arctic prison camp; his whereabouts were unknown for a number of days, causing a big scare among his family and supporters, and capturing the world's attention. Then on 15 February the Kremlin chose to show Navalny to the whole world, attending a video-recorded court hearing by video-link, in good health and in defiant spirits. The following morning he was announced dead. The official diagnosis given by prison authorities was 'sudden death syndrome'.

The body was promptly hidden; no meaningful excuse offered for hiding it from the family. Against that background, it is fair to say that the Kremlin's denials of complicity are evidently not intended to deceive, but to mock.

By this demonstrative execution of its best known political prisoner, whose death the US President had publicly vowed to avenge, the Kremlin sends an important message both to the West and to its own subjects. To the West it says: we don't give a hoot about your "devastating consequences". Anything you can be reasonably expected to say or do in response to this – from verbal condemnation to further economic sanctions – won't deter us from killing whoever we want. Indeed, hours before Western leaders even reacted to Navalny's death, the Russian Foreign Ministry was already circulating statements to condemn the West for condemning it.

And the message to Russians is this: don't hope that your opposition to Putin or to his war will merely land you with a 19-year term of imprisonment amidst worldwide protests, perhaps to be exchanged later for some Russian spies or POWs, or to be triumphantly released after the downfall of the regime. The penalty for political dissent in Russia is death.

Raising stakes in this way is hardly consistent with the picture painted by the Russian propaganda over the past two years – the picture of united fascist Russia rallied around its leader's agenda of world conquest and Patriarch Kirill's jihadist version of Christianity. The truth is that Russians responded to the invasion of Ukraine with an unprecedented nationwide storm of protest. When the Soviet Union invaded Czechoslovakia in 1968, seven people publicly protested at the Red Square in Moscow and were imprisoned for long terms – a pivotal moment in the history of the Soviet dissident movement which eventually finished the USSR off.

In the 1990s, rallies against the First Chechen War peaked at a few thousand – but protesting in those times was not much riskier than in Western democracies. This time, human rights organisations have recorded as many as 20,000 arrests for anti-war street protests in Russia, which is only a fraction of the total number of protesters, as not everyone was arrested and not every arrest was recorded. If seven protesters in 1968 shook the Soviet empire to its foundations, how should its heirs react to tens of thousands? This is not to mention the widespread arsons of conscription centres and dim rumours of mutinies in army units.

In a statement released from prison in response to the full-scale invasion of Ukraine in February 2022, Navalny appealed to Russians to go out to the streets to protest, and added "if, to stop this war, we have to congest the prisons and prison vans with our own bodies, we will do so". This is what thousands of Russians have been doing. If semi-public executions of leading prisoners cannot stop that process, nothing else can. Navalny was naturally top of the list; but there is little doubt that the lives of Vladimir Kara-Murza, Ilya Yashin, Alexei Gorinov, Mikhail Kriger and hundreds of other prisoners are now in graver danger than ever before.

Navalny's death, and other deaths which may well follow, mean a lot more than one of the many humanitarian issues which have arisen out of this war. It is a fateful move on the global chessboard. The outcome of the war and the future of Europe depends on being able to counter it effectively. Nothing less than 'devastating' will do. Putin will only laugh at verbal condemnations. He is also no doubt prepared for whatever still can be scraped out of the barrel of potential economic sanctions.

The only place where retaliation would really bite is the battlefields of Ukraine. The only thing that might impress and deter Putin is if every death of a Russian political prisoner promptly leads to a serious strategic disadvantage in combat. It is for military experts to say exactly how to achieve that, but the only Western response which Putin will notice is to give Ukraine something we have never given before and perhaps also to lift the restrictions previously imposed on using advanced Western weapons only in Ukraine but not on Russian soil. Anything less dramatic than this is foreseen and will be ignored.

Doing what little I can in response to Navalny's death, I am putting in place a standing order for monthly donations to the Ukrainian army. The amount will sharply increase every time another political prisoner dies in Russia, until the end of the war or my bankruptcy. I hope others will do similar things according to their own means, and that the governments will do a hell of a lot more. After all, this may be our last chance before the political terror in Russia escalates to Stalinist dimensions and the only hope of lasting peace in Europe is gone for a long time.

Pavel Stroilov is a Russian dissident who fled Putin's Russia to the UK in fear for his life 20 years ago. He is now a consultant to the Christian Legal Centre.