Boris Johnson is on Tuesday set to approve a deal to allow Huawei to build its 5G network, despite months of intense lobbying against the decision by Donald Trump's administration.
The Trump administration has spent months lobbying the U.K. against allowing Huawei into its telecoms network, amid concerns over its close links with Chinese intelligence.
Top Republican officials and former Trump aides warned the decision could rupture the U.K.-U.S. intelligence-sharing relationship and lead Congress to block a post-Brexit trade deal.
Boris Johnson is set to defy the United States on Tuesday and allow Huawei to help build the U.K.'s 5G network, a move which risks a major diplomatic row with President Trump.
Trump's allies have repeatedly warned that the move, which Boris Johnson is expected to confirm this afternoon, would risk a dramatic rupture in the United Kingdom's intelligence-sharing relationship with Washington, and could jeopardise the prospect of a post-Brexit deal between the two countries.
Tim Morrison, a former advisor to President Trump, warned on Monday that approving the Huawei deal could lead Congress to block a U.K.-U.S. trade deal.
"We are talking about allowing the Chinese Communist Party into the telecommunications system, into the healthcare data, into the personal financial records of every Briton," he told BBC Radio 4's Today programme.
"I'm concerned that, as the United Kingdom finally appears to be at least at the end of the beginning for Brexit, what this could mean for a U.S.-U.K. trade agreement."
However, Johnson has reportedly resolved to approve the deal anyway, saying that a "very important strategic win" was possible to provide consumers with faster broadband without "comprising our critical national infrastructure."
The decision will be formally taken at a meeting of the National Security Council on Tuesday morning and announced at around lunchtime.
Several House Republicans, including Liz Cheney, Jim Banks, and Mike Gallagher, also warned on Monday that allowing Huawei a role in the UK's 5G network could damage the intelligence-sharing relationship between the UK and US.
Both countries are members of the so-called Five Eyes countries, along with Canada, Australia, and New Zealand, who share their most sensitive intelligence with each other.
"Our relationship with the U.K. right now is among our very closest, if not the closest in the whole world," Cheney, the No. 3 House Republican leader, told Politico.
"I think that if they make the decision that if they're going to have Huawei in their 5G that we have to recalculate [and] reassess whether or not they can continue to be among the closest of our intel partners.
Her warning echoed that of Mike Pompeo, who along with Trump has been intensively lobbying Downing Street for the last few months over the decision.
But the White House has offered no public sign of how it will react to the Huawei news, raising the prospect that Johnson could successfully call Trump's bluff over the decision.
U.K. ministers hinted on Monday that the Huawei deal would contain concessions designed to placate anger from Washington and other allies over security risks.