Some British staff and dependants are being withdrawn from the embassy in Ukraine in response to the growing threat from Russia, the Foreign Office has said.
Boris Johnson warned that "gloomy" intelligence suggested Russia was planning a lightning raid on Kyiv as British staff and their families began leaving the Ukrainian capital.
Mr Johnson said he did not believe war was inevitable and there was a chance that "sense can still prevail", but confirming the exit of some British staff from the embassy, he said: "We do think it prudent to make some changes now.
"The intelligence is very clear that there are 60 Russian battle groups on the borders of Ukraine, the plan for a lightning war that could take out Kyiv is one that everybody can see," he said.
"We need to make it very clear to the Kremlin, to Russia, that that would be a disastrous step.
"I think it’s very important that people in Russia understand that this could be a new Chechnya."
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The United States has also ordered the families of all American personnel at the US Embassy to leave the country in response the the risk of an invasion.
But the European Union's foreign policy chief Josep Borrell said the EU would not "do the same" and Ukraine's foreign ministry spokesman Oleg Nikolenko said the US decision was "a premature step" and a sign of "excessive caution".
It comes after the UK accused President Vladimir Putin of plotting to install a pro-Moscow leader in Ukraine as he considers invading the country.
Deputy Prime Minister Dominic Raab also said there is a "very significant" risk Russia will mount an invasion.
"The world needs to keep its eye on this and be very clear with President Putin that it would not do this cost-free, that there would be a price," he told the BBC's Sunday Morning programme.