The shake-of-the-hands in front of the media on a blustery, wet spring morning in central London outside the official residence of British Foreign secretary Jeremy Hunt was friendly. America's secretary of state, Mike Pompeo, and Hunt joked about the weather.

Pompeo, on his first official visit to London as U.S. Secretary of State, had come to reaffirm the "special relationship" between Britain and the U.S., he said. "The special relationship does not simply endure, it is thriving," Pompeo announced at a news conference midweek following meetings with British counterpart Hunt and British Prime Minister Theresa May.

Britain US Pompeo FILE - U.S. Secretary of State Mike Pompeo meets with Britain's Prime Minister Theresa May, right, at 10 Downing Street in central London, May 8, 2019. FILE - U.S. Secretary of State Mike Pompeo meets with Britain's Prime Minister Theresa May, right, at 10 Downing Street in central London, May 8, 2019.

But for all the bonhomie, and later, at a research organization event, banter about how the first-born son of Prince Harry and his American bride Meghan Markle is the latest example of Anglo-American cooperation, Pompeo's trip was anything but routine. The visit exposed strains in a relationship that is being buffeted by sharp disagreements over policy toward Iran and Britain's dealings with China.

China's Huawei

America's top diplomat delivered a blunt public warning in London about doing business with China and specifically about using the technology of Chinese telecom giant Huawei to develop Britain's fifth-generation (5G) wireless network. He urged Britain to rethink its provisional decision to allow Huawei to have a role in building the network, warning that China wants "to divide Western alliances through bits and bytes, not bullets and bombs."

U.S. officials fear Beijing will use Huawei, which ultimately is answerable to the Chinese government, to eavesdrop and to sweep up data passing through Britain's 5G network. The prospect is alarming to U.S. security agencies. They fear Chinese spies will be able to penetrate American networks and even capture intelligence shared with Britain.

Pompeo emphasized that if Britain uses Huawei's pioneering technology for its 5G network, it would be putting at risk the longstanding intelligence-sharing arrangement it has with Washington — the rock on which the special relationship is built.

"Insufficient security will impede the United States' ability to share certain information within trusted networks. This is just what China wants — to divide western alliances," Pompeo warned.

British politicians have reacted cautiously to the U.S. threat to curtail intelligence sharing, an unusually overt warning for an American diplomat to deliver on British soil. They say they think they can square the circle — have Huawei participate in the development of parts of the next generation mobile network but in a way that answers U.S. security objections.

FILE - A staff member stands in front of a Huawei FILE - A staff member stands in front of a Huawei shop in Beijing, China, March 7, 2019. FILE - A staff member stands in front of a Huawei shop in Beijing, China, March 7, 2019.

Britain has said it is planning to allow the Chinese telecom giant to participate in a limited role in developing the 5G network. Officials talk about ensuring that Huawei's participation is kept in non-core areas. The decision was made by Prime Minister May, over the objections of her security and defense chiefs.

On Thursday, in an interview with a Chinese media outlet, the country's finance minister, Philip Hammond, downplayed U.S. worries, saying, "[Huawei] has responded very positively and confirmed that it is willing and able to address those concerns and ensure that those security defects are corrected for the future. So we're very pleased about that."

A former British foreign minister, and onetime chairman of the British parliament's intelligence committee, Malcolm Rifkind, told Britain's Sky News that disagreements between British and U.S. leaders aren't unusual.

"There's nothing new about that," he said. "Margaret Thatcher had rows with Ronald Reagan, John Major with Bill Clinton. It is the normal situation between friends. Occasionally you disagree."

He believes there's a work-around, pointing out that Huawei has been highly involved in Britain's current 4G network and its role is monitored by a team of British intelligence operatives "to make sure there's no mischief."

Deals with China

Monitoring, though, may not be enough to assuage U.S. worries, says a former senior counter-intelligence officer, who served in the agency's clandestine service for 33 years and asked not to be named in this article. He says there's increasing alarm in U.S. intelligence circles about Britain's readiness to accommodate China, a rising power seen in Washington as determined to weaken Western alliances.

"The Chinese don't distinguish between commerce, politics and espionage — it is all the same for them," he said. "The British are not on their guard enough, partly that's because they're desperate to get a major post-Brexit trade deal from Beijing and they don't want to do anything that might wreck that from happening," he added.

Britain is now the top European destination for direct investment from China, and some former and current U.S. intelligence officials worry the British are failing to scrutinize thoroughly business and infrastructure deals involving Chinese companies.

China is building nuclear power plants in Britain, and Chinese companies are being encouraged by the British government to bid for contracts to build and manage HS2, a high-speed railway that, when completed, will directly link London, Birmingham, the East Midlands, Leeds and Manchester.

FILE - China's President Xi Jinping addresses gues FILE - China's President Xi Jinping addresses guests and delegates at the UK-China Business Summit in Mansion House, central London, Oct. 21, 2015. China agreed to put down a 6 billion-pound ($9.3 billion) stake in the U.K.'s first nuclear power plant since the 1980s. FILE - China's President Xi Jinping addresses guests and delegates at the UK-China Business Summit in Mansion House, central London, Oct. 21, 2015. China agreed to put down a 6 billion-pound ($9.3 billion) stake in the U.K.'s first nuclear power plant since the 1980s.

If Britain does give Huawei even a limited role in building its future 5G network, the fallout would be similar to a major spy scandal, the former counterintelligence officer said. "Think Kim Philby," he said, citing the top British spy who was unmasked in 1963 as a double agent for Russia's KGB spy agency and whose betrayal undermined American trust in British intelligence for decades.

"Even if there's no formal decision to curtail intelligence-sharing, the consequence will be felt all the way down the line. People at Langley and in other [intelligence] agencies will have doubts and will start withholding information by not uploading it to databases the British can access," he added.

Britain is a key member of the so-called Five Eyes alliance, the U.S.-led Anglophone intelligence pact also linking Australia, Canada and New Zealand. Norman Roule, who was in the CIA's Directorate of Operations for 34 years, and served as a division chief and chief of station, says "the U.S. intelligence relationship with the British is the closest on the planet."

"We share so much information with each other, and it's shared so deeply and immediately that if we have a difference of views, it's usually because one of us hasn't gotten around to seeing the other's file yet," he added. He says on the Huawei issue, the British security agencies "don't have a different view than that of the United States."

He predicts there were will be weeks of technical discussions.

"The devil will be in the details," he said. "The question will be, 'Can you take some of Huawei's technology and put it in places where it doesn't matter and still guarantee security?'"