I saw a lot of Vladimir Putin when I was British ambassador to Moscow. He certainly was a rational actor then. Never had I dealt with a politician as clear, cold and calculating as the Russian president, comparable only to Margaret Thatcher in the thorough way he read his briefs. Putin quietly absorbed bad news and stored up his revenge for a more propitious time. Certainly he took risks, but the downsides of these were risks – such as the 2014 annexation of Crimea – had already been carefully and correctly costed.

That is why I believed that he would never actually go through with a wholesale invasion of Ukraine.

But the Putin of 2022 is a very different man. From his 5,000-word article “On the Historical Unity of Ukraine and Russia” to the rambling stream of consciousness of the speech that launched his assault on Ukrainian sovereignty, he has manifested an almost clinical obsession with bringing the country to heel. His references to the Ukrainian regime as “Nazis and drug addicts” have become almost demented.

As I talk to Russian friends, loyal to their country and keen to find sensible explanations for its conduct, I find increasing bafflement at the behaviour of their president. None of us anticipated that he would take the huge risk of all-out war. 

They are too careful to say so, but I am sure they share my assessment that, whether through extended Covid isolation or the sharply narrowing circle of advisers to whom he listens, Putin has let his obsession with Ukraine drown out his previously careful judgment of where Russia’s interests lie.

Three times so far he has implied the possible use of nuclear weapons in the context of Ukraine, shattering decades of convention among established nuclear powers not to talk about them. 

On the eve of the final diplomatic breakdown, Putin conspicuously staged full-scale nuclear exercises, including the launch of ballistic missiles. On the day of the invasion itself, he threatened any outsiders who interfered with “such consequences as you have never encountered”. At the weekend he publicly instructed his defence minister to place Russia’s nuclear forces on high alert.

Putin’s Russia, a global power, has joined history’s notable exceptions; Pakistan and India came very close to using nuclear weapons in 2000-2001, and Israel made preparations to deploy them during the 1973 Yom Kippur War.

The West has reacted with remarkable sang-froid to this sabre-rattling. Apart from reminding the Russians that we too have a deterrent, there has been little sign of real concern. 

This is because Putin is still presumed to be a rational actor. A real nuclear exchange would be as catastrophic for Russia as for the West. Surely, Western leaders might think, he is plainly engaged in a game of high-octane bluff (known in the jargon as being ready to “escalate to de-escalate”). His aim is to warn Nato off any direct intervention in the Ukraine war.

But is the same assessment true of a Putin driven by a sort of Pan-Slavic mysticism? It was the American Cold War thinker, Thomas Schelling who noted that the risks of negotiating with an irrational counterpart were higher because he may be less concerned by the potential cost to his own country than someone less ideologically driven would be.

So we should perhaps be a bit more careful on this issue. We should also take more notice of Russian military doctrine, which, in times of adversity, encourages short-term escalation to achieve long-term de-escalation.

We can take some comfort in the growing evidence that my concerns about the route Putin has chosen are increasingly shared by those around him. His normally impeccably choreographed Security Council showed distinct signs of unease as the assault on Ukraine was launched. Even leading oligarchs have publicly cast doubt on the direction Russia is now taking – which is unprecedented.

Maybe, as we launch our no-holds-barred, take-no-prisoners assault on the Russian ruling class, we should ask ourselves whether there might be potential allies there, who would be willing to displace Russia’s increasingly unbalanced autocrat.

Sir Tony Brenton is a former British ambassador to Russia