Crisis meetings were held in Britain because of concerns Vladimir Putin was close to deploying nuclear weapons in Ukraine in October 2022, an updated biography of Liz Truss claims.
The former prime minister was concerned wind would carry the fallout to British skies, according to the book Out of the Blue.
It says she spent her final days in office studying weather maps and preparing for radiation to hit Britain.
“Exquisite” US intelligence is reported to have concluded there was a 50 per cent chance Russia would deploy a tactical nuclear weapon in Ukraine or a larger one over the Black Sea.
Ms Truss spent “numerous hours studying satellite weather data and wind directions” because of fears the “wrong weather patterns” could have a “direct fallout effect on Britain”, the book by journalists Harry Cole and James Heale claims.
A separate and new book, War, by Watergate journalist Bob Woodward, reports that the White House believed there was a 50 per cent chance Russia would deploy a battlefield weapon based on the intelligence received.
That month Joe Biden, the US president, said there was a “direct threat” of nuclear weapons being deployed by Russia for the first time since the 1962 Cuban missile crisis “if, in fact, things continue down the path they are going”.
Ben Wallace, the then defence secretary, visited Washington DC for talks amid the crisis.
It comes amid fears Donald Trump, who returns to the White House on January 20, will force Ukraine to permanently give up Russian-held land for a peace deal.