Rhodri Marsden: Soothing, reassuring, accurate. No wonder we keep dialling 123

On his 1970 album 'Til the Band Comes In, Scott Walker sings of his unreciprocated love for the woman behind the Speaking Clock. He suggests their shared insomnia might form a basis for an ongoing relationship, and invites her – should she be listening – over to his place.

Walker was evidently unaware that the voice he knew belonged to a homely British Telecom employee 23 years his senior called Pat, but he wasn't alone in his adoration. Pat received bags of fan mail and marriage proposals during her 21 years as BT's voice of temporal accuracy, and her successor, Brian Cobby, soothed regular callers with his mellifluous pronunciation of the word "precisely". (If you fancy emulating Cobby, he attributed his vocal quality to gargling regularly with Worcestershire sauce. If, having read that, you no longer fancy emulating Cobby, I don't blame you.)

This week marks the 75th anniversary of the Speaking Clock, and our affection for it is both charming and mystifying. In my line of sight right now are five objects that can tell me the time – a mobile phone, a computer, a television, an oven, an MP3 player – and while none of them agrees precisely, each of them is capable of ensuring I don't miss a train or over-boil an egg. But we still dial 123 to listen to Sara Mendes da Costa (pictured right), the current voice of the BT clock, more than 30 million times a year. And we dial other, predominantly female, voices on competing networks a few million more.

We call for gentle reassurance in anxious moments when we can't trust our existing, plentiful supply of clocks; ie New Year's Eve, the change to and from British Summer Time, and waking up in the morning during a power cut and wondering why the hell the alarm didn't go off. In Norway, you'd be on your own; Froken Ur (Miss Clock) was taken out of service in 2007. In Finland, barely anyone calls Neiti Aika (Miss Time) any longer, and speaking clock services in the US are thin on the ground, too.

But here, you're just 31p (and I've always wanted to say this: other networks may vary) away from a clock that's guaranteed by the National Physical Laboratory to lose just one second in three million years. You might not need such accuracy to determine whether the chemist is still open, but boy, it's good to know that it's there.