(CBS News) The British Underground, better known as the "Tube," celebrates its 150th birthday this year. It is the oldest underground railway in the world, and one of the best known brands in Britain, but now it's getting attention for something very different, following an unusual request from a widow.

For retired doctor Margaret McCollum, the Tube is much more than a quick way to get around London and Embankment Station is no ordinary stop.

For the last five years, this has been the one place in London where McCollum could still hear the voice of her beloved late husband, Oswald Lawrence. McCollum said of him, "He was a larger-than-life character. He was terrific fun and he had a great zest for life."

More than forty years ago, Lawrence, a theater actor, became the voice of a travel announcement that any American tourist in London would instantly recognize: "Mind the gap...mind the gap..."

It's the safety message that plays on the Tube, warning travelers to watch out for the space between the train and the platform.

After Lawrence died, McCollum often came to Embankment -- the last station that still used his recording.

McCollum said: "So if I had time, I would sit and wait for the next train, so I can hear his voice again. ... It was just lovely. It's just very special listening to his voice after he died."

But then a few months ago, McCollum got a shock. She said: "Much to my sadness and horror indeed, last November when I was on the station, the first week of November, there was no Oswald. A few days later, still no Oswald."

Lawrence's message had been scrapped as the Tube updated its announcement system. McCollum decided to take action. She sent a letter to the London Underground asking for a recording of her late husband's voice. Moved by her story, the directors did one better -- retrieving Lawrence's distinctive, clipped tones from the archives and reinstating them at Embankment Station.

Nigel Holness, operations director of the London Underground, said: "We were delighted to help. And we went to, you know, through a lot of trouble to get the recording, get it installed again on the station. So it's a fabulous story."

Certainly, McCollum shares their enthusiasm. "I'm just delighted that we've got the results and here he is," she said. "He's never really far away in all sorts of senses, but this was a place where I could still come and hear his voice and that was very special and now he's back, which is wonderful."

And McCollum can go home, knowing that the next time she passes through, he'll be there.

Watch Clarissa Ward's full report in the video above.