The UK and its allies have been warned they must prepare for world war by the head of Nato amid increasing tensions between Moscow and Europe.

In a dramatic day, it emerged that a Russian submarine had been carrying out an “operation” in the Channel for three days while Moscow said British soldiers in Ukraine were legitimate targets.

It comes just days after a British paratrooper was killed in an accident away from the frontline. New Feature

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Tobias Ellwood, the former armed forces minister, urged caution and said the UK should not allow Vladimir Putin to “spook us.”

But Nato secretary-general Mark Rutte said that Nato had to be ready for a “scale of war our parents and great-grandparents endured”.

In a speech in Berlin, Rutte said th

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