The question “What will Putin do next?” is usually followed by: “Would Putin use a nuclear weapon in the Ukraine war?”

The Russian president has dropped some unsubtle hints.

On announcing the start of his “special military operation” – the full-scale invasion of Ukraine – he had issued a warning to “those who may be tempted to interfere from the outside”.

“No matter who tries to stand in our way or create threats for our country and our people,” the Kremlin leader declared, “they must know that Russia will respond immediately.

“And the consequences will be such as you have never seen in your entire history.”

Western leaders generally dismissed what they saw as nuclear sabre-rattling. Since the start of the war Western governments have crossed several Russian “red lines”: providing Ukraine with tanks, advanced missile systems and then F-16 fighter jets.

The “consequences” threatened by the Kremlin never materialised.

In September Putin announced he was lowering the threshold for the use of nuclear weapons – the decree was published this week. A clear warning to Europe and America not to allow longer-range missile strikes on Russian territory.

Now this red line, too, has been crossed. In his address to the nation Putin confirmed Western reports that Ukraine had fired US-supplied Atacms and British-made Storm Shadow missiles at targets inside Russia.

Earlier this week, when pro-Kremlin tabloid Moskovsky Komsomolets asked a retired lieutenant-general how Russia should respond to an Atacms attack on Bryansk region, he replied:

“Starting World War Three over strikes on an arms depot in Bryansk region would probably be short-sighted.”

It would be comforting to think that the Kremlin shares that view.

But Vladimir Putin’s address to the nation contained no evidence of that.

His message to Ukraine’s supporters in the West appeared to be: this is a red line I’m serious about, I dare you to cross it.

“Even Putin doesn’t know whether he can use a nuclear weapon, or he can’t. It depends on his emotions,” Novaya Gazeta columnist Andrei Kolesnikov told me recently.

“We know he’s a very emotional man. The decision to begin this war was also an emotional step. Because of that we must take seriously his idea of the changing of the nuclear doctrine. They say the fear of war must return and will contain both sides, but this is also a tool of escalation.

“In this interpretation we must admit that Putin, under some circumstances, can use at least a tactical nuclear weapon in the framework of a limited nuclear war. It will not solve the problem. But it will be the start of a suicidal escalation for the whole world.”

Tactical nuclear weapons are small warheads intended for use on the battlefield or a limited strike.