Deputy Prime Minister Dominic Raab said there was "a very serious risk" of invasion but there would be "severe economic consequences", including sanctions, if Russia took that step.

The deputy prime minister also assessed the threat of an incursion by Russian forces as "very significant", as he urged the Russian president, Vladimir Putin, to “ step back from the brink ”.

Raising the prospect of financial sanctions, Mr Raab told Sky News : "There will be very serious consequences if Russia takes this move to try and invade, but also install a puppet regime".

Last night, the Foreign Office took the unusual step of naming former Ukrainian MP and media owner Yevhen Murayev as a potential Kremlin candidate to take over in Kyiv, with four others, including a former prime minister and a former acting prime minister, among those who are supposedly to be given senior ranks.

In a statement, foreign secretary Liz Truss said the Russian plotting showed the lengths to which the Kremlin was prepared go to undermine the government in Kyiv.

"The information being released today shines a light on the extent of Russian activity designed to subvert Ukraine, and is an insight into Kremlin thinking," she said.

"Russia must de-escalate, end its campaigns of aggression and disinformation, and pursue a path of diplomacy.

As the UK and our partners have said repeatedly, any Russian military incursion into Ukraine would be a massive strategic mistake with severe costs."

We are in communication with the Russian government."

The Russian Foreign Ministry said Britain should stop spreading nonsense, but the British allegations do echo similar warnings made by the American government on Thursday.

However, he told the BBC's Sunday Morning programme it was "extremely unlikely" British troops would be sent to defend Ukraine, adding that the country was not a Nato ally.

He added that Russia "needs to live up to the basic tenets of international law and invading another country is not one of those".

Russia has denied it is planning any attack but Mr Putin has issued demands to the West, including that Ukraine be prevented from joining the Nato military alliance.

Dozens of British troops have been in Ukraine since 2015 to help train their armed forces, and the UK has also made a commitment to help rebuild Ukraine's navy following Russia's invasion of Crimea in 2014.

The Foreign Office's claims were thrown into further confusion when the man it named as a "potential candidate" as Moscow ’ s presidential pick told the Observer he would make an unlikely candidate to head a puppet government for Moscow.

"It isn't very logical.

I'm banned from Russia.

Not only that but money from my father's firm there has been confiscated," Mr Murayev said.

"Ukraine needs new politicians whose policy will be based solely on the principles of the national interests of Ukraine and the Ukrainian people," he said.

by Paul Adams, BBC diplomatic correspondent Stung, perhaps, by suggestions that while a crisis was boiling in Europe, the foreign and defence secretaries were both in Australia, the UK government does seem to be trying to show that it's getting a grip.

The Foreign Office has said that it had exposed evidence of a plot to install a pro-Moscow government in Ukraine, and Boris Johnson promised to "ramp up pressure on Russia", as his own domestic political troubles deepened.

The British Foreign Office seems confused," said former Ukrainian MP Yevhen Murayev, laughing.

the foreign office also said it had information on former ukrainian politicians who had links with russian intelligence services.

"some of these have contact with russian intelligence officers working on an invasion plan.

Earlier this week, the UK announced it was sending defence weapons and extra troops for training.

"given the last bilateral defence talks between the countries took place in london.

Commons Defence Committee chairman Tobias Ellwood warned a Russian incursion could be "imminent" as President Vladimir Putin looked to exploit Western weakness.

US secretary of state Antony Blinken held talks with Russian diplomats in Switzerland on Friday in a bid to avert a conflict on Ukraine's border, where Moscow has amassed an estimated 100,000 troops.

"We are prepared to put very severe sanctions in place, we are also working to support Ukraine in terms of defensive capability."

However four of the five men live in exile in Moscow, making their ties to Russia's leadership less a matter of subterfuge than public record.

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