U.K. telecommunications giant BT Group Plc admitted it has missed a government deadline to move data flows away from networking equipment provided by China’s Huawei Technologies Co. Ltd., and now faces the prospect of a heavy fine.

The company said in an update today that all 4G and 5G data sessions and voice calls are now being delivered by non-Huawei core equipment. According to Bloomberg today, that means more than 99% of its core traffic is now served by equipment provided by other suppliers. The remaining 1% of data and voice calls is on older 2G and 3G networks, the company added.

The company had until the end of last year to migrate its data flows away from Huawei’s gear. The deadline is for all of Britain’s telecommunications providers, but BT is by far the country’s largest provider of consumer broadband and mobile services, and therefore faced the toughest challenge in meeting it.

The costs of migrating away from Huawei’s equipment are huge. BT said the process involved migrating more than 30 million active customers, and has previously stated it will cost in excess of £500 million ($635 million).

The U.K.’s government banned the use of Huawei-supplied equipment within key parts of its telecoms infrastructure in 2020, citing national security concerns. The Chinese company had become a critical supplier to U.K. providers in the preceding decade, which meant BT faced an enormous challenge to rip it all out and replace it.

Ever since that announcement, BT has been rushing to replace the Chinese-made equipment used within its extensive network with gear supplied by the Swedish provider Ericsson AB. According to BT, it is making “good progress” on ripping out the remaining Huawei devices, but it hasn’t said when it expects the job to be completed.

Some of BT’s primary competitors, including Vodafone Plc, do not use any Huawei equipment in their core networks, while most of the others used very little. For instance, Hutchison 3G UK Ltd., parent company of Three UK, said it only had a small amount of Huawei-made equipment in its network and has already met the Dec. 31 deadline to swap it all out. Another key provider, Virgin Media, has also previously said it has replaced all Huawei gear ahead of the cut-off date.

The U.K. has threatened companies that miss the end-of-year date with fines of up to 10% of their revenue, or £100,000 for every day they aren’t compliant.

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