News of the destruction of Flight MH17 and the appalling murder of 298 people gave Russia’s president Vladimir Putin a chance to step back from a precipice. Yesterday, he could have stood up before the world and denounced the crime; endorsed a full investigation and punishment of the guilty.

Instead – yet almost inevitably, given the nature of the man – he presented his stone face. He asserted, against all logic and evidence, that Ukraine and its rulers were the guilty parties.

He lied, as he has lied all his life since he was first schooled in deceit and brutality by those masters of the art, his old employers at the KGB. Putin probably felt that no path was open to him save denial, because the facts point blame for this huge tragedy squarely at the Kremlin. In March, Putin annexed Crimea, then embarked on a strategy of covert military support for pro-Russian separatists in eastern Ukraine, designed to sustain civil war and ruin the country.

Month after month, Western intelligence has tracked Russian special forces – ‘little green men’, as they are nicknamed, because they wear no uniforms or badges – working with the pro-Kremlin separatists.

Satellite photographs show heavy weapons and tanks trundling into eastern Ukraine from Russia.

Whether the Malaysia Airways plane was hit by a missile supplied by Moscow or captured from the Ukrainian Army is neither here nor there. Putin is the sponsor and puppet-master of the rebels. Thus, he must bear responsibility for this appalling act.

His apologists say the rebels thought they were firing at the Ukrainian military. That, too, is irrelevant. Putin has placed deadly toys in the hands of recklessly irresponsible people. For months, observers have expressed fears that Putin would find the separatists impossible to micro-manage. So it has now proved.

For those – almost all of us – who have hoped since the end of the Cold War that Russia could join the fellowship of nations, pursuing the values of democracy and freedom, this is a sad day.

It confirms what has seemed increasingly apparent since the Ukrainian crisis erupted: Putin’s Russia is not merely no friend to the West. It has chosen to make itself our enemy.

On the credit side, there will be no return to the nuclear stand-off of the Cold War. Nobody among the Western powers wants to start shooting over Ukraine. But Putin becomes more dangerous every day, because he has boxed himself into a corner from which it will be hard, if not impossible, for him to escape. He has made Russia an autocracy in which free speech is a dead letter. It is now a crime to criticise the Red Army in history books as well as in modern speech.

All broadcast channels are state-controlled, and pour forth a torrent of deceits, not least about Ukraine. Russian viewers are obliged to feast on atrocity stories about alleged crimes by Ukrainian troops against Russian speakers, including public crucifixion of a three-year-old child.

In the mad world Putin has created, a dismaying number of his people are ready to believe such stuff. He may even do so himself: the Kremlin becomes ever more Stalinesque, with the president dependent for information and counsel on a slavish circle of intimates who tell him only what he wishes to hear. Enemies and critics are imprisoned after show trials, or liquidated by hitmen.

Unsurprisingly, Putin has failed in his efforts to modernise the Russian economy: 55 per cent of the nation’s budget now depends on foreign sales of gas.

Moscow’s Ukrainian adventure has caused growth forecasts to be slashed from 1.8 per cent to below 1 per cent this year, and at least £40billion of foreign capital has left the country.

Putin has constructed a narrative to explain all this: Russia is encircled by enemies, Nato and the EU foremost among them, forever seeking to extend their tentacles into Moscow’s rightful sphere of influence.

He said in March, justifying the Crimean annexation: ‘Russia finds itself in a position it could not retreat from. If you compress a spring all the way back to its limit, it will snap back hard.’ He tells his people that Russia is a proud nation, responding to Western threats, insults and expansionism.

So how should the West address this pocket Stalin? Since the end of the Cold War, US and EU diplomacy has been extraordinarily clumsy: wilfully humiliating the Russians; then making offers of partnership to Ukraine and other neighbouring states without considering their implications or impact on Moscow; and finally, responding feebly when Putin began to lash out.

But whatever the West’s mistakes in the past, these should not obscure the fundamentals today: Putin is a brute and a bully who must be shackled.

Since the spring, US rhetoric has been far more robust than that of Europe, and especially that of Germany’s Chancellor Angela Merkel. She seems morbidly afraid of taking any action that might tempt Putin to cut off her country’s gas supplies.

Back in March, the EU issued a solemn statement: ‘Any further steps by the Russian Federation to destabilise the situation in Ukraine would lead to additional and far-reaching consequences for relations in a broad range of economic areas.’

It seems hard for anybody in Brussels or Berlin to deny that the killing of 298 innocent people, most of them EU citizens, does indeed constitute ‘further steps’.

Putin has acted throughout his tenure of power on the assumption that European leaders are marshmallows, to be defied with impunity.

It is time, and beyond time, to prove him wrong. Baroness Ashton, the EU’s foreign policy supremo, has a last chance to show that she is not wholly ridiculous.

The first round of Western sanctions against Russia in the spring addressed only some named individuals. The list of Putin associates whose funds are frozen and whose family members are denied access to Western countries must be drastically extended, even if some of them own European football clubs and mansions in Kensington.

Graduated sanctions must be extended to Russia as a nation. France should refuse to continue construction of warships for the Russian Navy. There should be no EU finance for Russian projects. There must be a carrot and stick: if the Russians pull back from eastern Ukraine, they get rewards. Dangerous state enemies should always be offered a way out. But if Putin persists on his current path, his country has to be punished economically for his actions.

Even though the West is rightly unwilling to consider military action against Russia over Ukraine, iron-clad and very public security guarantees must be given to Poland and the Baltic states. It is just possible that Putin is reckless enough to raise the stakes, to try to create new regions of instability beyond his frontiers. He must be made to understand that if he does so, Nato will respond militarily.

Russia, and explicitly its president, are today complicit in an appalling crime in the skies over Ukraine. If the West fails to punish Putin for the ruthless adventurism which has caused this to happen, it will be a bad day for the security of us all. A cruel and dangerous man is rampaging on the Eastern horizon. If he cannot be checked there, how can we trust our governments to protect us from such threats nearer to home?