Donald Trump’s negotiators have signalled that the next prime minister’s hopes of a post-Brexit trade deal with the United States rest on his willingness to fall in line with tough American policies against the Chinese telecoms giant Huawei.

Whitehall correspondence seen by The Sunday Telegraph reveals that British officials close to transatlantic trade talks believe allowing Huawei to ­provide equipment for new 5G mobile networks could be a deal-breaker.

In one message a civil servant lifts the lid on how the controversy over the alleged threat to security posed by Huawei is intertwined with a web of diplomatic and trade concerns in Washington DC.

A British refusal to back curbs on Huawei would be viewed, for instance, as “undermining Washington’s efforts to reinvigorate the World Trade Organisation [WTO]”, the official warns.

The comment refers to ongoing efforts by American diplomats to reform the special status of “developing” economies under WTO rules.

Mr Trump has insisted China should no longer qualify for such preferential treatment as part of his trade war with President Xi.

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Further reports from preliminary trade talks between London and Washington appear to confirm suspicions in the telecoms industry that some US concerns over Huawei are based on matters of ­international commerce rather than national security.

Britain is yet to issue clear guidance to mobile operators of what, if any, Huawei equipment they may use in new 5G networks.

A Whitehall review has been stuck in the works for months, despite an unprecedented leak from the National Security Council suggesting Theresa May was prepared to reject American demands for an ­outright ban.

Emails from major telecoms companies to the Department for Culture, which is leading the review, and an arm of the spy agency GCHQ, which is providing technical advice, reveal mounting frustration as investment decisions are delayed.

Ministers and civil servants have been attempting to juggle complaints, and the need for investment in better mobile networks, with Britain’s hopes of a swift free trade agreement with President Trump after Brexit.

One senior official told The Sunday ­Telegraph the “US keeps ­moving the goalposts”. Last week, Washington dropped its plan for a blanket ban on US and ­US-linked companies working with Huawei.

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Instead, it will issue licences, in a move to de-escalate tensions with China following talks on the sidelines of the G20 meeting in Osaka last month.

Yet despite telecoms industry calls for Huawei to be given a broad reprieve, correspondence seen by this newspaper hints at genuine security fears. Specialists have complained to GCHQ about the Chinese company’s approach to fixing software bugs.

Huawei denies its equipment poses a security threat. Ben Wood, an independent analyst for CCS Insight, said the US position on Huawei was a “moving target”.

Delays to a UK definitive position on the security and political risks posed by the company was the “biggest challenge” facing network operators, such as Vodafone, he added.

It was also “extremely challenging for the likes of Ericsson and Nokia. It’s impossible for them to accurately assess what their addressable market will be and could trigger delays to the roll out of 5G”.

Nokia and Ericsson declined to comment on the evidence seen by The ­Telegraph. A Vodafone spokesman said: “We take security very seriously. Any decision should not be rushed, but follow a fact-based risk-assessed approach.”