A senior US official has met with Boris Johnson’s chief adviser Dominic Cummings in the hope of getting the government to change its mind over Huawei’s involvement the UK’s 5G network.

Donald Trump’s acting chief of staff, Mick Mulvaney today met with Cummings and the Prime Minister’s chief strategic adviser Eddie Lister in what sources described as “a very important meeting” with serious repercussions for the UK-US security partnership and future trading relationship.

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Johnson did not attend.

Although the Americans are said to be furious about last month’s decision to allow the Chinese firm limited involvement in the UK’s network, one source told City A.M. there was “a landing zone out of this”, if Downing Street made a firm commitment to “gradually eliminate [Huawei]… within the life of this government”.

The US position is said to be “frank and full-on” but ultimately constructive.

The adviser said the meeting should be a wake-up call for Number 10 to stop “hiding from reality”. If Downing Street sticks to its guns it would be “very difficult” to get a trade deal through congress, he noted.

“This is not just a case of a few words, and lip service, and the Americans will go away,” the source said. “This is a real dispute and it has to have real answers. This is a matter of vital national importance to the US and we need to understand that – I don’t think officials have done yet.”

Separately the government is being petitioned by a growing number of high profile backbench Tories, who are concerned about the involvement of Huawei in critical infrastructure.

Although they are keen to play down talk of a rebellion, pressure is being applied both in public and behind closed doors to have it overturned.

MPs including Iain Duncan Smith, Tom Tugendhat, Owen Paterson, David Davis, Damian Green, Tobias Ellwood and Bob Seely have joined forces to push back against the decision.

“This is not a Brexit thing. We have people who were Remainers and people who are Brexiters – all wings are covered,” said one of the MPs involved. “There is a general disquiet about the peculiar nature of threat Huawei poses to us.”

The Huawei decision is just one of a number of thorny issues putting tension onto the relationship at a critical time. Others include the UK’s plan to forge ahead with a digital services tax, which is due to come into force in April.

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At Davos last month US Treasury secretary Steve Mnuchin describe this approach as “discriminatory in nature” and warned of reprisal taxes if Downing Street forges ahead with the plan.

Downing Street declined to comment further as City A.M. went to press.