Video report by ITV News Political Correspondent Daniel Hewitt
Boris Johnson has decided to allow Huawei to be involved with the UK's 5G network, after receiving conflicting advice.
On one side, the prime minister had been told the technology firm is safe, but on the other is the US, which claims British sovereignty would be put at risk if the firm were to play a role in the UK's 5G infrastructure.
Here's a look at the key questions surrounding Huawei and 5G.
What is Huawei?
Chinese technology giant Huawei is the world's second-biggest smartphone manufacturer and one of the world's biggest suppliers of telecommunications equipment.
It says it is a private company "wholly owned" by its employees, but questions have been raised about the mechanics of its ownership structure.
It was founded in 1987 by Ren Zhengfei, who, before his career in industry, worked in the engineering branch of the People's Liberation Army.
Why is the company controversial?
Huawei has come under scrutiny over allegations of close ties to the Chinese state.
Founder Mr Zhengfei's past links to the military have been cited as a concern, as has China's history of state sponsorship and surveillance.
Chinese law can also compel firms to co-operate with Chinese national intelligence work, which some critics have suggested could see Beijing require Huawei to spy on people through so-called "back doors" in its telecoms equipment.
Huawei has vehemently denied the allegations of any ties to the Chinese state and says it abides by the laws of every country in which it operates.
Why is Huawei so important to 5G?
Huawei has invested billions of pounds into research and development around 5G network infrastructure and, as a result, is now considered the industry leader in 5G technology.
It is also already part of the existing network infrastructure in a number of countries, including in the UK.
As a result, using one of Huawei's rivals, and most likely alternatives - Ericsson or Nokia - for the building of 5G networks, is likely to cause a delay and add cost to the introduction of widespread 5G in the UK.
In contrast, none of the four largest mobile carriers in the United States use Huawei equipment in their networks.
How have the UK's allies approached the issue?
The UK is a part of the Five Eyes intelligence network, which also includes the United States, Canada, Australia and New Zealand.
The US has previously banned Huawei from its government networks, and last year imposed restrictions which limit Huawei's ability to trade with US companies.
The US has publicly urged its Five Eyes allies to do the same, and Australia has also blocked Huawei from its 5G networks.
What does Huawei say?
Huawei has always denied having ties to the Chinese government, with the company's founder denying that Beijing has ever asked his company to help spy on its clients.
Mr Zhengfei, in an interview last year, said: "I love my country. I support the Communist Party. But I will not do anything to harm the world."
He said Huawei had never been asked to share "improper information" about its partners by the government.
"I personally would never harm the interest of my customers, and me and my company would not answer to such requests.
"No law in China requires any company to install mandatory back doors."
What does America say?
The United States has warned that British sovereignty would be put at risk by allowing the firm to play a role in the UK's 5G infrastructure.
US Secretary of State Mike Pompeo described the choice facing the Prime Minister Johnson as "momentous" in a last-ditch plea to ministers who are expected to make the call on Tuesday.
The US administration has previously urged allies in the Five Eyes intelligence community - made up of the US, UK, Canada, Australia and New Zealand - not to use Huawei, claiming it would be a security risk - something the company vehemently denies.
Mr Pompeo, who is due to visit the UK later in the week, said: "The UK has a momentous decision ahead on 5G.
"British MP Tom Tugendhat gets it right: 'The truth is that only nations able to protect their data will be sovereign'."
He retweeted a comment by Mr Tugendhat, chairman of the Commons Foreign Affairs Committee in the last parliament, in which the MP said: "The real costs will come later if we get this wrong and allow Huawei to run 5G."
In an urgent Commons question Mr Tugendhat warned that the UK should not be "nesting the dragon".
"If even the Communist Party in Vietnam rejects it, deciding to set up its own network and reject Huawei, perhaps we should beware of strangers and the gifts they bear," he said.
Washington's ambassador to the UK, Woody Johnson, said Mr Tugendhat's point was "undeniable", adding that "doing 5G right goes beyond data 'mitigation' - it's about national sovereignty".