Vladimir Putin is the Hitler of the 21st century. His actions in Ukraine are a nasty replica of the German invasion of Czechoslovakia which began in 1938.

The smouldering sense of grievance at the loss of empire, the Russian citizens in Ukraine who need to be “protected”, the manufactured incidents, mercenaries dressed in Ukrainian uniforms in order to strike from within, the threats against those who might intervene. The comparisons are all there.

A deranged bully does not stop. If Ukraine is recaptured by the Russian Empire how safe is Estonia? Or Georgia? Or Poland?

It is essential for those who believe in democracy, freedom and the rule of law that the Russian invasion of Ukraine does not succeed.

“Cometh the hour, cometh the man” could have been coined for President Zelensky. His attitude, his communication skills, his visible and brave leadership have already led the people of Ukraine to a point where, in the long run, Russia will not prevail. How can an invading army of perhaps 200,000 soldiers permanently subdue a defiant nation of over 40 million people – it cannot, but it might take years and much blood for the Ukrainians to win their freedom again.

The key question is rather, what can we do right now to save Ukraine from tyranny and show Russia that 20th-century behaviours will not succeed in Europe in the 21st century?

The sanctions against Russia are already having a marked effect on the country; its stock market and currency are close to collapse as it is progressively excluded from international financial systems. Ordinary Russian people rather than Putin will suffer the consequences. Unfortunately, as the price of oil and gas rises, Russia earns ever more in foreign exchange.

If we are to avoid an escalation into a wider war we probably should not put our combat forces in the air over Ukraine but, if we are to stop Russia in the short term rather than the long, we must arm Ukraine with our best weapons so they can fight its invaders on more equal terms. That, however, is not enough – we must be prepared to act decisively and quickly to make Russia a pariah state.

Russia should be completely not just partly disconnected from the international financial system. Our banks should be forbidden from taking deposits from or lending to Russian customers. Existing deposits connected to Russia should be frozen. Our citizens and companies should be forbidden from purchasing Russian assets. Russian companies should be ejected from all stock markets in all democratic nations. Exporting to or importing from Russia should be banned. Russians, unless they would face persecution at home, should be sent back to Russia.

The key though is energy. We have to be brave enough to take the crucial step of not buying Russian oil and gas. Will that be painful? Yes it absolutely will but that pain would be nothing when measured against the potential cost of stopping the bully later rather than now.

As quickly as possible we must wean ourselves off the dependency on fossil fuels – the dependency which Russia is exploiting now. We must up the pace in deploying renewable generation capacity and becoming more energy efficient. Nuclear generation must come back on the table as a vital bridge to a fully sustainable energy world.

Right now though we need to get the coal-fired generating plant in Europe back on line. We need to licence new oil fields in the North Sea, we need to incentivise energy producers to maximise their short-run production levels – and we should make sure the tax on the profits from these is used to pay for a more rapid transition away from fossil fuels and vulnerability to the whims of a despot.

This is a test for the core values we hold and we must not fail Ukraine or ourselves.

Guy Stenhouse is a Scottish financial sector veteran who wrote formerly as Pinstripe