"We've looked at their posture. There isn't a significant change," he said on LBC radio, accusing Putin of trying to "flex muscles" with his invasion of Ukraine bogged down.

Wallace said he had assured his 12-year-old son: "No, we're not going to have a nuclear war.

"What I've said to him is, look, President Putin is dealing at the moment in a rhetoric, he wants to distract from what's gone wrong in Ukraine, and he wants us all to be reminded that he has a nuclear deterrent."

But Britain, France and the United States had their own nuclear deterrence available, Wallace stressed: "It's kept us safe for decades. It is a deterrent by definition and design."

The minister said the progress of Russia's advance into Ukraine was deteriorating, telling BBC radio in a separate interview: "There are many reports of Russians either sort of deserting or surrendering.

"Because they are confused as much as anyone why they are engaged in a war with people they're probably related to."