LONDON — The U.K. is too dependent on the United States for its defense and has not adequately invested in a back-up plan should the U.S. pull away from Europe, a damning report by a cross-party group of lawmakers warned Wednesday.

A report by the House of Commons Defence Committee says the U.K. could be left in a vulnerable position if a global crisis sees America pull away from its traditional role of militarily backstopping Europe. Britain needs to see where it could replace U.S. capabilities “in the event of them being withdrawn,” it urges.

While noting that many European nations upped defense spending after Russia’s full-scale invasion of Ukraine in 2022, the committee argues that “both resourcing and capacity for European alternatives to U.S. provision are still a challenge.”

U.S. President Donald Trump has long urged European countries to commit more resources to the NATO military alliance.

“If Europe fails to respond in a timely manner, there may well be a crisis elsewhere in the world which results in the U.S. withdrawing capabilities from Europe overnight and Europe being left vulnerable,” the committee says.

The report also argues that the U.K. lacks a clear plan for defending both itself and its overseas territories in the event of an invasion. It slams decision-making at the Ministry of Defense as “slow and opaque.”

“We have repeatedly heard concerns about the U.K.’s ability to defend itself from attack,” said Labour MP Tanmanjeet Singh Dhesi, who chairs the committee. “Government must be willing to grasp the nettle and prioritize homeland defense and resilience.”

Prime Minister Keir Starmer has pledged to spend 5 percent of GDP on national security by 2035. On Wednesday his Defense Secretary, John Healey, talked up Britain’s response to a “new era of threat,” as Starmer’s government attempts to tie defense spending to a broader industrial revival.