UK Prime Minister Boris Johnson is expected to allow Chinese tech giant Huawei build out its fifth-generation mobile networks in Britain, the Financial Times reported, citing people close to the discussions.

A final decision on Huawei's future role in the UK will be taken at the National Security Council on Tuesday. Johnson is looking at imposing a cap on Huawei's market share, FT said.

A minister for the government has previously told CNBC security will be the "top priority" ahead of the decision.Washington has long tried to persuade London to ban Huawei.

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The US government claims the Chinese company poses a security risk, and threatens UK-US intelligence sharing, saying that allowing Huawei on the market would be "madness."

US Secretary of State Mike Pompeo wrote on Twitter on Sunday night that the UK had a "momentous decision ahead on 5G."

"The security and resilience of the UK's telecoms networks is of paramount importance," a UK government spokesperson told CNBC. "The Government continues to consider its position on high risk vendors and a decision will be made in due course."

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Huawei has consistently said that it is a private company and is not subject to Chinese state interference. It has warned the UK that by caving in to American pressure, it may see its own technological development fall behind on a "fabricated pretext."

Three out of four of the UK's big carriers (EE, Vodafone and Three) already use Huawei equipment in the networks. Vodafone says that it doesn't use Huawei in its "core," and has "multiple layers of security and encryption in place between it and our masts."

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