Ahead of a decision on whether to allow Huawei to supply some "non-core" parts for the UK network, a US delegation has presented the UK with new evidence claiming to show the security risks posed by the Chinese firm.
A decision is expected to be taken later this month, but what's wrong with Huawei, and are they a company we can trust?
Here's everything you need to know about the situation:
What's so bad about Huawei?
The technology company has come under fire in recent months, particularly in the US where Donald Trump continues to attack the Chinese firm.
Last year, Trump issued an executive order blocking transactions involving information or communications technology that “poses an unacceptable risk to the national security of the United States", describing the company as "something that’s very dangerous".
At the same time, the US Department of Commerce announced Huawei had been added to an index of companies and people deemed a threat to American security.
US intelligence agencies including the National Security Agency (NSA), FBI and CIA have previously implored American citizens to avoid using Huawei smartphones and services over fears the company may pass user data back to the Chinese government and engage in espionage.
Google also revoked Huawei's access to its Android operating system, though Huawei confirmed it would continue to support its smartphones and tablets with security updates and services.
The Chinese firm also developed its own operating system in response to the Android ban, an open-source software called HarmonyOS which can be adapted for use across a wide variety of electronic devices.
Richard Yu, chief executive of Huawei's consumer business group, described HarmonyOS as "trustworthy and secure", and announced the new system will be shipped with Huawei's smart screen products, such as TV sets, later this year in China, before being rolled out to other countries.
Will the UK ban Huawei?
On the campaign trail ahead of last December's general election, Boris Johnson has gave his strongest hint yet that he was planning to ban the Chinese firm from building Britain's 5G mobile networks, after discussing the US issue with the President.
At the Nato summit in Watford, Donald Trump lobbied the Prime Minister and other world leaders to exclude Huawei from crucial national infrastructure.
Johnson told a press conference: "I don't want this country to be unnecessarily hostile to investment from overseas.
"On the other hand we cannot prejudice our vital national security interest, nor can we prejudice our ability to co-operate with other Five Eyes security partners and that will be the key criteria that informs our decision about Huawei."
In May 2019, Theresa May give Huawei limited involvement in building the UK’s forthcoming 5G network, angering ministers who favoured a total ban on the company’s equipment.
Robert Strayer, the deputy assistant secretary for cyber at the US State Department, said the UK’s decision represented an “unacceptable risk” to security because of its links to an “authoritarian government”.
A senior Government official insisted that no final decision had been made and pointed out that totally excluding Huawei would make it harder to build a comprehensive 5G network in the years to come, because so few firms are equipped to do it.
What do Huawei have to say?
On the issue, a Huawei spokesperson said: “We’re confident the UK government will continue to take an objective, evidence-based approach to cyber security.
"Our customers trust us because we supply the kind of secure, resilient systems called for by the Nato Declaration and will continue working with them to build innovative new networks."
Huawei has repeatedly denied all allegations its equipment could be used for espionage and ties to its native government, beyond paying taxes.
What if I already own a Huawei phone?
Whatever the government's decision is, it will not affect those who already own a Huawei phone.
The decision is on whether to allow Huawei to supply some "non-core" parts for the UK network; if the government decides against Huawei, alternative parts and tech will have to be found from other suppliers.
The 5G network will still go ahead, and all phones will be able to work off it; the current 4G network remains unchanged.