The Defence Secretary has warned the UK must be prepared to go to war without the US as its principal ally.
Speaking to the Sunday Times, Ben Wallace said if America withdraws from international leadership, under President Donald Trump, previous assumptions which have underpinned UK defensive strategies may need re-thinking.
Mr Wallace said the prospect of America backing away from that role is something that keeps him awake at night.
"I worry if the United States withdraws from its leadership around the world. That would be bad for the world and bad for us. We plan for the worst and hope for the best," he said.
It comes as the Prime Minister is gearing up to lead what has been described as the "deepest review" of Britain's security, defence and foreign policy since the Cold War.
Mr Wallace told the Sunday Times the UK should use the review to identify and develop new capabilities, in order to lessen its dependence on the US.
He said, "we are very dependent on American air cover and American intelligence, surveillance and reconnaissance assets. We need to diversify our assets."
Cover image: The Defence Secretary, Ben Wallace (Picture: MOD).