The leak of this apparent decision was attributed to the then defence secretary and disgruntled China hawk Gavin Williamson, prompting Mrs May to sack him. But Mr Hunt’s comments on Thursday suggest Mrs May’s cabinet may be planning to revisit the issue, or is at least looking for a way to assuage US concerns.

The Five Eyes partnership, which also involves Australia, New Zealand and Canada, is a linchpin of Australia’s national security – and Britain, with its hugely capable intelligence services, is a key player. Any threat to British participation in the Five Eyes would be viewed with alarm in Canberra.

If you can’t get your closest allies to trust you, it doesn’t matter whether you can manage the risk or not. — Tom Tugendhat MP, Foreign Affairs Committee chairman

Mr Pompeo, formerly the head of the CIA, was in London for the day to hammer home his warning that the British government’s apparent inclination to allow Huawei into parts of the country’s 5G network could trigger an American pull-back from sharing intelligence with Britain, its closest Five Eyes partner.

“The US has an obligation to ensure the places where we operate, places where US information is, places where we have national security risks, that they operate within trusted networks – and that is what we will do,” Mr Pompeo told the press conference.

Could the Five Eyes be at risk?

Australia and New Zealand have followed the US in banning Huawei from participation in their 5G networks. Canada has not yet made a decision, but is said to be considering following Britain’s more flexible approach – which the US and Australia worry makes their networks vulnerable.

The Five Eyes partnership is extremely robust but not entirely unbreakable, said John Hemmings, director of the Asia Studies Centre at the London-based Henry Jackson Society.


“If the technical vulnerabilities are such that they threaten US and Australian national interests or security then inevitably there will be a gradual degrading of what is shared, and that will be a tragedy for Britain and for the other four,” he said.

Tom Tugendhat, a Conservative MP and former military officer who chairs the UK Parliament’s Foreign Affairs Committee, told The Australian Financial Review that this worried him deeply.

“I think it’s hugely concerning, because the Five Eyes relationship is fundamentally based on trust,” he said. “Injecting doubt into a trust-based relationship can undermine the fundamentals of the partnership. Particularly at a time when the liberal order is in question.”

Ian Levy, the technical director of Britain’s National Cyber Security Centre, which is a unit of the signals intelligence agency GCHQ, argued in a blog post recently that it was possible to run a secure 5G network in which not everything was protected to the same level.

“5G changes things in interesting ways from the way we do things today, but not in a way that fundamentally breaks all our current security principles and paradigms,” he wrote.

Britain has managed Huawei’s involvement in the 4G network through a “cell”, called the Huawei Cyber Security Evaluation Centre (HCSEC), which brings together Huawei staff and GCHQ experts to identify flaws in the Chinese giant’s equipment that could make it vulnerable to exploitation.

“The model has worked pretty well for the past eight years,” Mr Levy wrote. “Because of this mitigation model, the UK operators that use the HCSEC have unparalleled information to help them manage the risk of using Huawei kit.”

Mr Tugendhat said even if the British government thought it could mitigate the risk using a distinction between core and edge, this was almost beside the point. “If you can’t get your closest allies to trust you, it doesn’t matter whether you can manage the risk or not,” he said.