Chief cyber security officer stated that Huawei's "bad" engineering practice means its mobile network equipment could be banned in Westminster and other sensitive parts of the UK.
Dr. Ian Levy, GCHQ, told BBC Panorama that the Chinese telecom div also faced what he described as the "brains" of the 5G network.
The British government is expected in May to find out whether to restrict or even bail 5G technology.
Huawei said he would deal with the problems.
Last month, GCHQ's security review of the company said that it would be difficult to manage Huawei's future products until it eliminates shortcomings in cyber security processes.
He added that technical issues with software development approach had led to vulnerabilities in existing products, which in some cases were not fixed, despite being identified in previous versions.
In his first interview, head of telecommunications equipment department company said plans to spend more than $ 2 billion already devoted to the "transformation program" to address identified problems.
"We hope to turn this challenge into a forward-looking opportunity," said Ryan Ding, executive director of the Huawei business group.
"I believe that if Huawei can run this program as planned, Huawei will become the strongest player in the telecommunications industry in terms of security and reliability."
However, Dr. Levy – Technical Director of the National Cybersecurity Center GCHQ – said he was not yet convinced.
"Security in Huawei is like nothing else – engineering like in 2000 – very, very bad.
"We have not seen anything that would give us the confidence that the transformation program will do what they say they will do."
He added that "geographical constraints – maybe there is no Huawei radio." [equipment] in Westminster "is now one of the options for ministers to consider.
Mobile UK – an industry group representing Vodafone, BT, O2 and Three – warned that preventing Huawei from engaging in UK 5G introduction could cost the country's economy up to 6.8 billion pounds and delay the launch of a new generation network up to two years.
Those who already use Huawei's equipment have decided to stay outside the core of their networks, performing tasks such as device ID verification and deciding how to direct voice and data.
EE has used Huawei's equipment in its 3G and 4G core, but BT currently eliminates it after buying a company.
The industry, however, wants to use Huawei's radio access network (Ran) equipment – including antennas and base stations. They allow individual devices to wirelessly connect to mobile data networks via radio signals transmitted over the aerial waves.
Communication on paper
The US is concerned about any application of Huawei products.
"You would never know when the Chinese government decides to force Huawei … to do things that would be in the best interest of the communist party to be heard by the United States," says Mike Conaway, a member of the Intelligence Committee.
Last year, the Republican drafted a law on banning the US government to operate with companies using the company's equipment. It was later adapted to become part of the National Defense Authorization Act, which Trump was signed by law.
The consequence was deterring the major telecommunications networks in the country from working with Huawei. The Chinese company is now suing an American government claiming that this move is unconstitutional.
The congressman now has a look at the UK.
"It's obviously a great link between Great Britain and the United States – the English speaking countries – important for maintenance," Mr Conaway told Panorama.
"But as part of that, we will have to estimate what risks they would have to share … the secrets that would pass Huawei's equipment, the Huawei network.
"In old school ways, we can always share the way you know paperback back and forth, but in terms of electronic communication, Huawei's Huawei network, at best it would be risky."
This is a thing that goes beyond political divisions.
Mark Warner, Democrat and Vice President of the Senate Intelligence Committee, also warned that Huawei will not be part of the UK's 5G network.
"I think the consequences could be dramatic," he said.
"I think there may be real worries about the possibility of a complete sharing of information because of the fear that the network that will be subjected to 5G in the UK may be vulnerable."
However, Dr. Levy GCHQ has rejected such fears by saying that efforts to digital communication meant that even if someone succeeded in intercepting them, they would only get "gobbledygook".
"Everything that is sensitive to a company or government or defense is independently encrypted in the network," he explained. "You do not trust the network to protect you, protect yourself."
He added that in spite of finding vulnerabilities in one of the Huawei's packages, "we do not believe that things are the result of the Chinese abuse of the state."
For its part, Huawei says the Chinese government will never ask for it to install backdoor or other vulnerabilities in its foreign customers' systems, and even if such a request was made, he would refuse.
And Mr. Ding has rejected suggestions that this obligation will be reduced if the US and China go to war.
"Here we have a country that practically does not use Huawei equipment and even does not know if our 5G equipment is square or round, but it is constantly expressing concern about security due to Huawei," he said.
"I do not want to speculate on whether or not they have a different purpose with this kind of thing. I would rather focus on the limited time I have to create better products."
Panorama: Can we trust Huawei? will be broadcast on BBC One at 8.30 pm this Monday.