BT and Vodafone would need at least five years to phase Huawei out of their UK networks if they are to minimize service outages and other disruption for existing customers, senior technology executives told a parliamentary committee today.

The new warning comes as authorities consider more stringent measures against the Chinese vendor following US moves to choke off its supplies of components made with American equipment or design expertise.

Amid concern Huawei poses a threat to national security, the UK government in January proposed restricting it to 35% of any radio access or part-fiber broadband network and banning it from the "core," the control center of the entire system.

Officials are worried it will not be able to find secure alternatives to semiconductors it buys from TSMC, a Taiwanese firm that uses US equipment. Some analysts think Huawei will run out of the necessary components early next year.

Heavily reliant on Huawei's equipment, BT and Vodafone have previously argued that a ban would cost "hundreds of millions" and hold up the rollout of 5G services, upsetting the UK's economic recovery from the coronavirus pandemic.

Under the restrictions proposed in January they have been given until 2023 to be fully compliant, but executives from the companies today painted a bleak picture if they are not allowed a much longer transition period in the event of a total ban.

"I would say a five-year transition plan would be the minimum," said Andrea Donà, Vodafone's head of networks. Trying to replace the Chinese firm in a shorter timeframe would be highly disruptive for customers and businesses, he told officials, resulting in sporadic blackouts for mobile phone users.

Vodafone also appears to have revised upwards its cost estimates of a swap-out after Scott Petty, the chief technology officer of the UK business, last year told reporters that a ban would mean "hundreds of millions" in rip-and-replace costs.

Quizzed about the costs today, Donà reckoned the final bill would be in the low single-digit "billions" as Vodafone is forced to rip out not only 5G but also 4G equipment to prevent the interoperability problems that could result from using two different vendors between those systems.

Vodafone was unaffected by the January proposals because it avoids Huawei in its core and uses its products for only about a third of its mobile sites, with Ericsson supplying the remainder.

Howard Watson, the chief technology and information officer of the UK's BT, broadly concurred with Donà's assessment and told the committee that a seven-year timeframe would be more realistic.

"It is logistically impossible to get to zero in three years," he said. That would mean blackouts for customers. We would not recommend going down that route."

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BT is even more dependent on Huawei than Vodafone, using its products at about two thirds of its UK mobile sites, including those in urban areas. It also uses Huawei in the core, although the company remains confident it will complete its switch to Ericsson by 2023.

Earlier this year, BT told investors that complying with a 35% cap on Huawei in radio access and fiber broadband networks would cost about £500 million (US$633 million), booked over a five-year period.

A total ban would add only "tens to hundreds" of millions in incremental costs, said Watson today, because some of the 4G equipment is old and needs replacing in any case.

"We think we can get to 35% without significant disruption," said Watson. "To take them all out would require multiple sites to be turned off for at least a day and sometimes two days. We would need to close streets, bring in cranes. That is logistically not practical in a timeframe of three years."

Both BT and Vodafone resisted suggestions they take advantage of "overlay" technologies to build their 5G networks with a different vendor from the 4G supplier, an option that some equipment vendors are now promoting as a potential fix.

"If I take an overlay to existing 4G it is not an immediate process," said Donà. "I need to build 5G coherently with the 4G stack I have to maintain the customer experience."

With its current spectrum holdings, BT would not be able to build a 5G overlay and provide a high-quality experience to its subscribers, said Watson. Operators that have done this in Asian markets have had much larger frequency assignments than are available to UK mobile operators, he said.

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— Iain Morris, International Editor, Light Reading