Chaos-hit Boris Johnson missed a vital phone call with Vladimir Putin due to being engulfed by fallout from the Sue Gray parties report.
The Prime Minister had been expected to speak to the Russian leader at 4pm on Monday to tell him an invasion of Ukraine would be "an absolute disaster for the world".
But the call was hastily postponed - and did not happen by the end of the night - after Downing Street revealed police were investigating 12 lockdown parties in No10 and Whitehall.
Boris Johnson ’s spokesman insisted on Monday that the PM was “still due to speak to President Putin” but admitted it “may slip to tomorrow”.
“I don’t know if we had a settled time, if I’m honest. It may be that the timings had to move around because we received the report today,” the spokesman said.
He added “I don’t know” if No10 had asked Moscow to reschedule the call, as sources told the Mirror’s Pippa Crerar. Sources suggested Moscow was unable to rearrange a new time.
Hours later, Britain's diplomacy was dealt another blow as Foreign Secretary Liz Truss - who was meant to accompany Mr Johnson to Ukraine tomorrow - tested positive for Covid.
Labour claimed the Prime Minister's diplomatic initiative was in "disarray" as he prepares to fly to Ukraine on Tuesday for meetings and a press conference with President Volodymyr Zelensky.
Shadow foreign secretary David Lammy said the reports showed there were "real world consequences" of having a prime minister fighting for his political survival.
"Amid a dangerous crisis threatening peace in Europe, a vital diplomatic opportunity has been missed as Boris Johnson scrambles to hold on to his job," he said.
"These are the real world consequences of a distracted Prime Minister unfit for office running a government in disarray."
Mr Johnson had been due to speak to Mr Putin before flying to Kyiv. But he spent much of the day preparing for and delivering a Commons statement on Ms Gray's pared report on lockdown parties in No 10 and Whitehall.
The Prime Minister's official spokesman said it was not unusual for the timing of calls between world leaders to change.
"You will appreciate the control of the timing for the receipt of this report rightly (was) with Sue Gray and her team, and the Prime Minister had committed to come to the House to make an update," the spokesman told reporters at Westminster.
Earlier, during a visit to Tilbury docks in Essex, Mr Johnson said he intended to urge Mr Putin to "step back from the brink" and not mount an invasion of his neighbour.
"I think Russia needs to step back from the brink," he said.
"I think that an invasion of Ukraine, any incursion into Ukraine beyond the territory that Russia has already taken in 2014, would be an absolute disaster for the world, and above all it would be a disaster for Russia."
Mr Johnson said that any Russian invasion would be "bitterly and bloodily resisted" by the Ukrainian people.
Foreign Secretary Liz Truss, who is due to travel with the PM, unveiled plans to beef-up sanctions on Russians should the Kremlin invade.
New legislation will be the "toughest sanction regime against Russia we have ever had", she told MPs.
"It will go further than ever before,” she told the Commons. “Until now the UK has only been able to sanction those linked to de-stabilisation of the Ukraine.
“This new legislation will give us the power to sanction a broader range of individuals and businesses."
“Golden" UK visas for Russian millionaires with links to Putin’s reigme will be reviewed before April 5, she said.
Measures include the power to freeze assets of individuals linked to the Russian state and deny them entry to Britain.
The United Nations Security Council met in New York at the request of the US to discuss Russia's troop build-up.
Russia's ambassador to the UN, Vasily Nebenzya, claimed talk of war was provocative, and said Moscow frequently deployed troops in its own territory.
China's UN ambassador said Beijing did not view Russia's troops near the border as a threat and urged all parties to not aggravate the situation.
