James Cleverly, the UK foreign secretary, told Conservative Party members on Tuesday that the government was ready to join any western response should nuclear weapons be used on the battlefield in Ukraine.
Pointing to what he saw as Russian President Vladimir Putin's sequence of strategic errors, Mr Cleverly said that any use of nuclear weapons would lead to consequences.
“We need to make it very clear that his sequence of strategic errors has got to stop,” he said on a panel.
“We will continue to support Ukrainians in the defence of their homeland and stand up for the international rules and norms.”
In recent weeks, Russia has ordered a partial military mobilisation and warned of using “all means we have” in the conflict — which many have interpreted as a threat to use nuclear weapons.
Asked how Britain would respond to the use of tactical nuclear weapons by Russia, Mr Cleverly told a fringe event at the Conservative Party conference that he could not go into detail but there would be a response.
“It would inevitably be the case that the use of nuclear weapons by any country anywhere in the world would not go without a response,” he said. “I'm not going to discuss the nature or the threshold.”
Kremlin spokesman Dmitry Peskov said Moscow did not want to take part in “nuclear rhetoric” spread by the West, while Mr Cleverly said the country had been left increasingly isolated globally.
One effect of the conflict has been a scramble to find new ways of bridging differences between European nations, with London seeking new opportunities for a reset in ties with Paris.
“I have no doubt that we will find ways of working brilliantly closely with France, and I have no doubt we’ll find ways of having blazing rows with France, because that’s what the Brits and the French do, it’s our thing,” observed Mr Cleverly.
Asked about French President Emmanuel Macron’s European Political Community, Mr Cleverly said he agreed with “recognising there is more to Europe than the EU”.
“I think having European countries finding ways to work together, whether on mutual security, economic security etc, etc, that’s certainly something we’ll go into with open eyes,” he said.
“We want to find ways of working well with our neighbours and partners and friends in Europe, and we’re willing to explore what this can do and how it can add value to our relationships.”
Prime Minister Liz Truss’s move to attend a meeting on Mr Macron's initiative in Prague, which came after days of weighing up whether to go, will raise eyebrows, given her explicit scepticism about the project only a few months ago as Mr Cleverly’s predecessor at the Foreign Office.
Mr Cleverly said it had struck him how much the international community has pulled together since Russia’s invasion of Ukraine, saying Mr Putin has failed in his aim to fracture the allies’ relations.
He said Russia’s veto on the UN Security Council is “problematic”, but that it still serves an “important function” as it “allows the world to see that they are isolated”.