The iconic speaking clock is apparently making BT around £21 million a year, with the 74-year-old technology still proving remarkably resilient.

Although it has been hijacked by the likes of Lenny Henry (in the name of charity) and, controversially, Tinkerbell for a sponsored tie-in, there have been just four main speakers in its entire history.

And with 70 million calls a year, at a cost of 30p per call, that amounts to a staggering profit for an automated phone line.

Popular

"It's hard to say why the speaking clock is popular," a BT spokesperson told TechRadar.

"The speaking clock has been around for 74 years so a lot of people have grown up with dialling 123.

"BT's speaking clock is a national institution, viewed with great affection by the general public."

Today the talking clock is accurate to within five thousands of a second, a far cry from the original accuracy of one-tenth of a second and it still influences timings for Big Ben and the News at Ten.

You can read about the history of the speaking clock in a special TechRadar Feature