Yes, to the left is a photograph featuring one of the unquestioned giants of British broadcasting, standing in front of a portrait of Lord Reith, the BBC’s first director-general. You’ll notice a number of things. Sartorial standards in the Corporation have slipped somewhat since Lord Reith's day. He never remembered to wear his BBC pass. I have a lot less paperwork to worry about than he did, and I will soon have the same amount of hair.

What, you may ask, was I doing goofing around in the hallowed Council Chamber of BBC Broadcasting House, under the portrait of the man credited with fashioning the public-service broadcasting ethos that still pulses through today’s BBC?

The story began in these pages. A while back I wondered whether Radio Times readers had any recollections of the SOS messages that I remember from years gone by. They always seemed to be on just before the news. In sparse language and serious tones they shone a brief, bright light on some unfolding human drama. “Would Mr and Mrs John Smith believed to be travelling around Cumbria in an Austin Maxi, please contact the hospital in Winchester where Mrs Ethel Smith is dangerously ill”. A telephone number would be read out, and that was it.

We were all left to wonder, while the pips played and the news began, whether Mr and Mrs Smith ever made it to that far-off bedside. Would poor Ethel die alone? Perhaps she pulled through and would go on to die in a freak accident 40 years later, run over by a car driver distracted by an SOS message on the radio?

We were never told. SOS messages were the most intense, personal moments in broadcasting. They used the power of radio and its ability to reach millions instantly to reach out to one or two individuals to tell them something that mattered only to them. But what happened to those people, we never knew. Which is why I asked RT readers for their experiences.

There was a big reaction. Many readers recalled hearing the messages. Others found themselves in the position of rushing to bedsides. One reader was a young girl when she fell very ill and an appeal was made for her parents to return home.

It was 1958 and six-year-old Linda Miller was staying with her auntie while her parents went off on holiday to London. Linda became very ill with what was initially suspected to be polio, but turned out to be a bone infection. She was taken into hospital in Sunderland, while an SOS message was broadcast in the hope of finding her parents.

They never heard it. But thankfully a cyclist by the name of Mr Clampit did. He remembered the details of their number plate from the broadcast and tapped on the car window when he spotted the vehicle in a car park. As a result, mum and dad made it to young Linda’s bedside and, after several months of treatment, she was released from hospital and grew up to be the kind of beautiful person who buys Radio Times.

I will not spoil the broadcast by over-trailing here the other RT readers who kindly agreed to tell us their stories for And Now an Urgent SOS Message. But I was moved by much of what I heard and I wish we’d had more time on air to dwell on their experiences. People were happy to share some personal, life-changing moments, and I want to thank here everyone who wrote, and everyone to whom we spoke.

The BBC archive revealed a great deal I didn’t know. For instance, the SOS system dated back to the earliest days of the British Broadcasting Company in the 1920s. John Reith saw the public-service possibilities of the messages and helped craft the rules that governed them. While the initial broadcasts could include missing persons (and pets), the system was honed to target only those who were dangerously ill. I know some people suspect dangerously ill was code for a person who had already died, but that’s an urban myth. There were strict rules to ensure that just before an SOS message was broadcast, a phone call was made to the hospital in question to ensure that the subject of the message was still with us. If the person had died, the message was cancelled.

Messages could be broadcast only once. No exceptions. And the BBC judged that it would be wrong to broadcast any follow-up to an SOS message, which is why we remained in the dark about what happened next. Auntie Beeb was keen to protect the individuals involved from prying inquiries. But the archive reveals that checks were made internally on how many SOS messages were successful.

You may be pondering when you last heard an SOS message. Not in the past decade, certainly, but exactly when I don’t know. Having successfully traced the birth of SOS messages thanks to the detailed paper trail that dates back to the BBC’s first moments, there is no certainty about when or why they stopped. No sign of a memo axing them. We’ve asked the people who would know, but it seems a combination of emerging technology (mobile phones) and Radio 4 schedule changes meant there was no more need for those chilling broadcasts.

I learnt a few other things in making our programme. In a note from the archive, from 1923 or 1924, there was word of the Daily Express demanding that the BBC be closed down. Plus ça change. And I discovered that John Reith himself wrote a weekly column for Radio Times. Finally something I had in common with him, besides being Scottish. We wrote for the same magazine. And for the same fee.

And Now an Urgent SOS Message is on tonight at 8:00pm on Radio 4