The UK Government has warned of a more than one in four chance that Russia will attack a British ally as a Nato chief has called on the West to "prepare for an era of war".
In an official risk forecast, ministers revealed that the UK would be forced to trigger a military response to counter Russia.
It comes as top Nato military officer Rob Bauer told the West to be ready for anything in a chilling warning.
Speaking to reporters after a meeting of Nato defence chiefs in Brussels, Bauer said we "have to realise" that peace is "not a given".
The UK Government has warned of a more than one in four chance that Russia will attack a British ally
PAExperts in the Cabinet Office have now created a National Risk Register to assess the biggest threats to the UK in the next two years.
It found that the likelihood of Russia, described as an "adversary state with a large, advanced military", attacking a non-Nato ally was higher than 25 per cent.
Earlier this week, the head of the Army warned civilians that they would need to be called up if a war breaks out with Moscow.
While the army battles with dwindling numbers, General Sir Patrick believes there should be a "shift" in the mindset of the public who will step up to defend the UK.
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Government officials said that in such a scenario "to contain and deter further aggression, military, diplomatic and economic capabilities will be needed".
They added that the resulting war would spark "disruption of supply chains" and higher fuel prices, damaging the economy for "several years".
Carlos Del Toro, one of America’s most senior defence officials, also echoed warnings.
He told journalists: "I think it is important for the United Kingdom to reassess where they are today given the threats that exist today."
Nato admiral says peace 'is not a given' in chilling warning: 'Not everything is going to be hunky dory'Downing Street was forced to deny any suggestion of a conscription with a spokesman saying that "hypothetical scenarios, talking about conflict, are not helpful."
Rishi Sunak’s spokesman insisted that there were "no plans" for a draft and that "hypothetical scenarios, talking about a conflict, are not helpful".
James Heappey, the Armed Forces Minister, added the UK had long-standing plans to "mobilise volunteers" but said "nobody is thinking" about a draft.