BT in 2017 signalled its intention to retire the copper-based public switched telephone network (PSTN) by the end of 2025.

"As part of this whole process, we're now taking the significant step of ending the sale of new analogue services across the UK," Openreach said in a blog post on Tuesday.

"That means from today, when customers sign up for a new contract - or when they switch, upgrade or re-grade their service via their provider - they'll be moved onto a new digital line rather than an analogue one."

Britain's Gamma Communications said the impending PSTN switch-off was driving early growth in its cloud-based PhoneLine+ product, which can replace the simple single line used by small businesses.

Gamma Chief Executive Andrew Belshaw said demand was increasing, but making the change was not a high priority for busy business owners, such as plumbers.

"One of the things we need to do is make sure that our customers get it a little bit higher up their list, so they're not caught out in a couple of years' time," he said in an interview after the company reported a 13% rise in first-half pretax profit.

"There's no reason you can't start switching now."

(Reporting by Paul Sandle; editing by Sarah Young)