A Chinese-owned company is making circuit boards for the top-secret next generation F-35 warplanes flown by Britain and the United States, Sky News can reveal.
Exception PCB, a printed circuit board (PCB) manufacturer in Gloucestershire, south west England, produces circuit boards that "control many of the F-35's core capabilities", according to publicity material produced by the UK Ministry of Defence (MoD).
This includes "its engines, lighting, fuel and navigation systems", it said.
When asked about the firm's Chinese ownership, the MoD said Exception PCB is an established manufacturer of circuit boards to the defence industry and presents "no risk" to the F-35 Joint Strike Fighter supply chain.
A director from the company said there are "clear firewalls in place" between Exception PCB and its Chinese parent company Shenzhen Fastprint.
But defence experts, including former defence ministers, expressed concern that a Chinese-owned company is producing any parts for such a classified, British and American fifth generation programme, because of long-standing fears about Chinese espionage and rivalry.
They said it is a particularly odd situation given President Donald Trump's trade war with China and his opposition to any involvement by another Chinese company, Huawei, in fifth generation civilian mobile phone networks.
"We have been completely and utterly naive about the role of China and it is only now that people are beginning to wake up," said Sir Gerald Howarth, a former Tory defence minister.
There is no suggestion that Exception PCB or Shenzhen Fastprint have done anything wrong.
The Chinese state has long been accused of seeking to steal details on the multi-billion-pound F-35 programme, headed by US defence giant Lockheed Martin.
The stealth aircraft, fitted with a suite of highly classified sensors and other technology, will form a core part of US, British and other allied air and naval forces for the coming decades.
Companies in nine countries that partnered on the programme from its early stages supply components for the entire fleet of aircraft that is being built.
This means parts made in the UK are put on F-35 jets flown by the US, Japanese, Norwegian, Italian and other militaries.
The revelation that one Chinese-owned firm is part of this global supply chain raises the possibility there could be others.
Lockheed Martin was unable to state categorically this was not the case.
"We are not aware of any other Chinese-owned F-35 suppliers at this time," the firm said.
A March publication by the UK MoD, entitled Small and Medium-Sized Enterprise (SME) Action Plan, promoted Exception PCB as an example of a UK-based firm that is part of the supply chain for the F-35.
What it did not mention is that Shenzhen Fastprint - a company based in China and listed on the Shenzhen Stock Exchange - bought Exception PCB in 2013.
Describing its involvement in the aircraft programme, the MoD publication said: "Gloucestershire-based Exception PCB manufacture the circuit boards that control many of the F-35's core capabilities."
A news article published by the MoD last November again promoted Exception PCB's F-35 credentials as part of an event called "Small Business Saturday".
It said the company's 107 employees "manufactured the circuit boards that control many of the F-35's core capabilities, including its engines, lighting, fuel and navigation systems".
An MoD spokesman this week played down the firm's activities when asked about its Chinese ownership and what due diligence the UK had carried out.
"Exception PCB produces bare circuit boards and as a result there are no risks associated with their product in the F-35 aircraft supply chain," he said.
Lockheed Martin, however, signalled there could be a limited risk.
It described Exception PCB as a "third-tier" supplier because its products go via another company, GE Aviation, before reaching the aircraft.
"Exception PCB produces bare circuit boards with no electronics to GE Aviation," it said.
"These parts, like all components on the F-35, are inspected repeatedly at each stage of manufacture. Additionally, Exception PCB has no visibility or access to any sensitive programme information and there is limited to no risk associated with their minimal role in the programme."
It added: "Should Exception PCB be determined an unapproved source in the future, GE Aviation has alternate sources of supply that would ensure no impact to the programme."
A director at Exception PCB had initially been happy to talk on camera about the firm's F-35 work and show Sky News around its plant on an industrial estate in Tewkesbury.
But the request was denied when Mike Devine sought approval from his boss and from GE Aviation.
He responded on Friday night to emailed questions sent the previous day.
Mr Devine said Exception has had a close partnership with GE Aviation since the 1980s and promotes its Chinese ownership.
"We produce bare circuit boards only in the UK for all of our aerospace and defence companies and have no visibility or access to the design data nor drawings for the boards. All that is supplied from any customer is manufacturing data," he said.
"This is 'dumb' Gerber data containing only information to enable Exception to produce only the bare PCB's, no additional electronic information is applied or supplied".
Mr Devine said measures are in place to ensure no Chinese national can access F-35 related information.
"All data is secured on a separate internal server and access to data is protected by passwords, only accessible by a selected few, of which have been audited by GE," he said.
Clark Ince, a director of Hallmark Electronics, another printed circuit board manufacturer in the UK, said firms make boards according to a design given to them by their customer.
He said he thinks it is possible for a company that buys another firm to glean details of what the circuit boards on its acquisition's order books might be used for even if - as in the case of Exception PCB - it is simply bare circuit boards for the F-35.
"They can look at certain designs and probably recognise what it's used for. If it is similar to what they are making but of a better design then they will copy it," he said.
It is also possible to embed technology such as a chip without a customer's knowledge into a circuit board that could affect the way it functions, he said.
Asked whether he thought there was a risk to allow a Chinese-owned company to make circuit boards for the F-35, Mr Ince said: "Yes I think so, personally I think so."
Documents on Exception PCB's website show that the company has also done work on other sensitive defence programmes including the Eurofighter Typhoon fighter jet, operated by the Royal Air Force, the US military's F-16 warplanes and the Apache attack helicopter.
An MoD source said the firm has been involved in Lockheed Martin's F-35 programme since its inception almost two decades ago.
Defence and security experts said it is surprising that a Chinese firm was allowed to acquire a British company with these kind of defence contracts.
"I think it's breath-taking," said Bob Seely, a Tory MP and army reservist who co-authored a paper about concerns on China's Huawei and Britain's 5G mobile network.
"It's not a question of: Is this bad? But it's a question of: How bad is it?" he said.
Mr Seely has raised the matter with Defence Secretary Penny Mordaunt in a letter.
In it, he said: "Will you consider a supply chain review for defence and military equipment?
"May I ask how many firms that bid for UK defence contracts are owned by firms from authoritarian or potentially adversarial states?
"I believe this example is symptomatic of a wider problem about how open and free nations deal with China's growing economic and digital power.
"It is clearly vital to continue to seek good relations with China given its expanding influence, but we need to be mindful that the Chinese state has a very different world view to our own.
"Whether it is in relation to 5G comms and Huawei, or this instance of a Chinese-owned firm now producing equipment for the F35, we need an urgent national conversation about how we deal with high-tech from authoritarian and potentially adversarial states."
Paul Beaver, a defence analyst, said there can be a blurring of the line between commercial entities and the state in China, which is particularly relevant when it comes to defence.
Beijing "believes that commercial companies in China are part of the state effort", he said.
"What people are concerned about - and I'm one of those - is if you have anything with a Chinese connection at least it ought to be known and the risks need to be assessed… To have it in the world's first fifth generation strike aircraft I think is really a cause for concern."
Lockheed Martin said there are no "direct F-35 suppliers based in China or under Chinese ownership". This does not include indirect suppliers like Exception PCB, however.
"We work closely with our industry partners to manage the F-35 Global Supply Chain in accordance with rigorous defence acquisition standards to ensure no parts and components from unapproved sources are included in aircraft production," Lockheed Martin said.
GE Aviation said it "works closely with all of our suppliers to ensure rigorous compliance with defence acquisition standards, export regulations and all legal obligations, including the F-35 supply chain.
"Exception PCB - a commonly-used industry supplier - produces bare circuit boards in the UK for GE Aviation and has no visibility to the design or drawing of the F-35 system."