It's unclear what penalties, if any, BT may face for this. The UK's telecoms firms were given formal legal warnings by the government in November 2022, telling them to bin kit from China's Huawei, after the US claimed, without evidence that the company was a security threat.

The firms were given a deadline of December 31, 2023 to stop using Huawei kit in their core networks. This was a delay from the previous deadline of January 28, 2023, which some firms (including BT) had moaned they would struggle to meet.

Now it seems BT has now missed this delayed deadline, although the firm says that only a tiny bit of the voice and data services it carries are now affected.

All 4G and 5G data sessions and voice calls are now delivered by non-Huawei core kit - meaning that over 99 percent of all core traffic is now being served by non-Huawei kit, a BT Group spokesperson said.

The only voice and data services yet to be moved are 2G and 3G, which make up less than 1 percent of its total traffic, the firm claimed.

It is thought that telecoms firms face being fined up to 10 per cent of its turnover for failing to follow the legal warning, or in the case of a continuing breach, £100,000 daily.

But any such action is unlikely to be taken straight away, as the country's telecoms watchdog Ofcom has first to report on how well network firms have done on meeting these goals, and the report is not due until 31 March this year.

"The government is in charge of setting and enforcing the rules requiring certain telecoms firms to remove Huawei kit from their networks. Ofcom's job is to collect information on firms' progress and report this to Government," an Ofcom spokesperson said.

BT had said following the rule to remove Huawei from its network would cost it an estimated £500 million between 2020 and 2025. All Huawei kit must be junked from the UK's 5G networks by the end of 2027.

It is not yet clear if other telecoms firms have missed the deadline for their core networks. We asked around, but had not got replies by the time of publication. All will likely be made clear by Ofcom's report in March.