It’s just before three in the afternoon. The moment before it happened. Shoppers are coming in and out of John Menzies, and Radio Rentals, and Milligan’s the bakers.

The Number 180 bus to East Kilbride has just pulled up outside. It’s a rainy day and a couple of old ladies are sheltering in a doorway.

The shoppers are the kind you would expect on a Thursday afternoon in the early 1970s: mostly housewives and retired people. Agnes Henderson, 78, who’s popped down with her 76-year-old sister Emma Brander. Thirty-year-old Maureen Hume, a name you might have recognised in the 70s; she was Scotland’s women’s badminton champion. And also there is 25-year-old mum Karen Fisher who’s left her two young kids with a neighbour so she can go out for some messages.

In one of the shops on the precinct, Malcolm Campbell the fruit merchant, the 18-year-old shop assistant Shirley O’Brien is speaking to the man from the Gas Board. For the last couple of days, people have been complaining about a smell of gas and the employee of the Gas Board has come to investigate. He tells Shirley there’s nothing to worry about.

Outside, more workers from the Gas Board have arrived and are digging holes in the road to see if they can find out what’s wrong. They’re being watched by 60-year-old Cyril Ewart from the window of the Castlebank laundry on the other side of the street. Cyril doesn’t know why, but he has a strange feeling as he stands there at the window surveying the scene: the workers, the shoppers, the No 180 bus.

It happens two minutes later. At 2.52pm. There is a loud rumbling sound. Then a bang. The windows of the laundry and other buildings are blown in. Glass everywhere. Cyril runs out into the road, but the air has filled with a dark cloud of smoke and dust. He can’t see a thing. He’s struggling to breathe. Through the dust he can hear people screaming and calling for help.

Glasgow Times:

The smoke clears to reveal the disaster. Ten of the shops in the precinct are gone, reduced to rubble. A man comes staggering over the stones. It’s 23-year-old salesman Thomas Henderson. Thomas had been parking in the car park on the roof. All he remembers is an awful bang and the roof giving way underneath him. His car slithered down on to the rubble but Thomas managed to get out and clamber over a pile of bricks and stone and metal and reach the pavement. It was one of the most remarkable escapes that happened that day: Thursday. October 21st, 1971.

Others are trapped. Like Shirley O’Brien, the shop assistant who was told by the Gas Board that there was nothing to worry about. “There was a rumbling and a bang and everything came down,” she said. “I was buried. Two men came and helped me out.” She also remembers looking back and realising that there was nothing left of her shop; it was gone.

Glasgow Times:

There were many other stories like Shirley’s: people who were nearly killed or injured, around 100 in all. Then there were the people who never got out. Twenty-two people died in the explosion at the shops at Clarkston Toll in 1971. Agnes Henderson and her sister Emma. Maureen Hume, the badminton champion. Karen Fisher, the young mum who’d popped out to get some messages. And 18 others, including Agnes Sands, a friend of Karen’s, a 14-year-old girl, Christina Wallace, and Etty Pattullo, wife of a local sheriff. John McDermott, 47, and Michael Freeman, 51, also died but mostly it was women. Young women. Young women with families.

Exactly 50 years after the disaster, I’m speaking to Karen Fisher’s brother Neil MacPherson, who was 13 at the time and lived in Knightswood. He remembers the day he heard what had happened. It was a holiday weekend and he’d just got home from school. His mum told him there’d been an explosion in Clarkston. He remembers there were rumours it might have been an IRA bomb. “I went to bed that night,” he says, “and my mother told me ‘I don’t think you’ll see your sister again’.”

In the end, Karen’s body was the last to be taken out of the rubble. Her friend Agnes had been in one shop and Karen was in another and because she was downstairs it took longer for the rescuers to reach her. More than 100 police officers and 20 fire-brigade units attended the scene, as well as every available ambulance in Glasgow. One by one, the casualties were taken to the Victoria Infirmary and Hairmyres, where every available doctor and nurse was called in for duty.

Glasgow Times:

Eventually, Neil and his parents and his three older siblings knew that Karen had definitely been killed. For a while, there had been some hope as the rescuers did their work. At one point, just a couple of hours after the blast, a policeman with a loudspeaker addressed the crowd of almost 400 that was gathered round the disaster zone. “Will every person remain still,” he said. “Do not move.” For five minutes, the firemen and the police anxiously listened for cries from the rubble. But there was silence. Soon afterwards, another body was located and taken from the ruins.

One of the traumatic moments that Neil remembers most vividly is the phone call that came on the Friday afternoon. “There was a call that my father took asking for someone to go to Mill Street in Paisley where the mortuary was. My father, who was an exceedingly strong man, didn’t go – my two eldest brothers went and identified her.” Eventually, the authorities also returned Karen’s personal effects which included her watch. “You might think they would clean it up,” says Neil. “but it was stained with blood. The watch had stopped at about 8 o’clock so my mum worried that was when she died.”

That thoughtless moment when Karen’s blood-stained watch was returned is just one of the things that Neil thinks would be done differently nowadays. “No one would get away with anything now,” he says. “There would be questions asked all day long for a week and that would set the tone whereas then it was a news incident, front page of the paper, and then no one saw any more about it. It would have been better organised and there would be better equipment and maybe they would have found more people faster – I don’t know.”

Neil also believes the inquiry that happened after the explosion was inadequate. A fatal accident inquiry was held but it concluded that no one was to blame. “The fatal accident inquiry concluded in about three months; it would take about ten years today to get all the evidence and tests together now. My parents weren’t even asked to take part. How can you have a gas leak for a week complaining about the smell, the gas board there digging holes and whatever else and people walking past with cigarettes and god knows what else and not be to blame for it?”

In the end, the conclusion of the experts answered some questions but not all. William Gibb, a forensic fire investigator and expert witness, pieced through the evidence and unearthed a fractured gas pipe under the pavement in front of the shops. The reason it had cracked is that it was insufficiently supported underneath so that when traffic was travelling past it, the ground was flexing slightly and that, combined with corrosion, caused it to crack. The gas from the pipe percolated through the soil and filled the large cellars underneath the shops and something then ignited it. Exactly what that was cannot be known for certain.

Fifty years on, Neil MacPherson sometimes worries that an accident like Clarkston might happen again. He, and other relatives of the dead and injured, are also concerned that there is still, in their view, no appropriate or sufficient memorial. I speak to Fiona Warrender, who was a schoolgirl at the time of the disaster and whose mother May Skellon was seriously injured. Fiona has campaigned for a proper memorial for many years and finally succeeded in having a memorial tree planted at Clarkston Halls. There is also a plaque at the shopping precinct. But it’s not enough, she says.

Neil feels the same way and says he believes East Renfrewshire Council want to forget about the disaster and move on. The council tell me, however, that they are planning a minute’s silence on the day and a special service at the memorial tree. Betty Cunningham, the deputy provost, says it was a dark day for Clarkston. “Many lives were lost,” she says, “and countless more were changed forever, so it is extremely important that the day is marked and we remember those who were lost. The commemoration at the memorial tree will give the families of victims and the survivors an opportunity to pay their respects and the minute’s silence will allow everyone to stop in a moment of reflection.”

Glasgow Times:

As far as Neil and Fiona are concerned, however, it should be better, and a decent memorial is the least that can be done, in their view, for the people who lived through the disaster, and the ones that didn’t, and their friends and relatives. Neil tells me about the shock he felt. He was 13 years old. And he tells me about his mother. She never got over it. And his father, who hid the grief deep down as Scottish men often did in those days.

Sadly, all these years later, no pictures survive of Karen but Neil remembers her vividly. He remembers the double funeral that was held for her and her friend Agnes. He remembers a policeman on the street taking his hat off and bowing his head. And 50 years on, he wants us to remember what happened to Karen Fisher and the other 21 people who were killed. And the men and women who were hurt and traumatised and shocked and survived by the skin of their teeth. This Thursday [21st], it will be exactly 50 years since it happened. Another Thursday, like the Thursday in 1971. 2.52pm. A good time to remember.

On the October 23rd, 1971, The Herald’s Dorothy Grace Elder attended the scene of the disaster and wrote about what she found. Her piece is reproduced here:

A tray of cakes and rolls still lay among the rubble in the shattered City Bakeries shop at Clarkston yesterday, a pathetic reminder of the everyday normality which exploded so horrifically on Thursday.

Yesterday Clarkston Toll was a place where local people moved around like automatons; a community where everyone I spoke to used the word “stunned”. What were once attractive modern shops lay like a deck of smashed concrete cards. Workers picked among the rubble, spurred on by the memory of other disasters where life had been discovered after hope was gone.

But, at around 3pm, almost exactly 24 hours after the heart of this busy suburb was ripped out, an eerie hush fell on the scores of policemen, helpers, onlookers, and journalists. Another body had been found.

There can be few sights more sad than that of an ambulance which does not hurry. Slowly, the cream vehicle backed up against a shattered shop and the crowd stood in heavy silence under the beating rain as a body wrapped in green tarpaulin was placed in the ambulance and the vehicle slowly nosed out through the crowd.

The road from Glasgow to Clarkston Toll passes prosperous redstone villas and the green sweep of a fine golf course, and it is with a sickening feeling that one comes upon the aftermath of the disaster – the devastated shops; the shattered glass in the gutters; the huge lorries and rubble-removing equipment; the massive hole outside a laundrette where Gas Board men toil in the mud and the tired, sad-faced policemen politely directing inquirers

It is now almost impossible to image this blitzed, tragic mess as being, such a short time ago, a promenade for shoppers and pram-pushers. Only a handful of shops remained open yesterday, where solemn-faced housewives quietly bought necessities.

The tragedy has been particularly hardfelt by women, and there was the common thought among housewives I spoke to that almost anyone of them might have been “down at the shops” on Thursday afternoon.

One shopper, Mrs Rae Fell, of Kirkville Drive, expressed the view of many when she told me, “I would have been down here if it hadn’t been such a rotten day. There is the thought that the disaster would have been even worse if Thursday had been a sunny day, bringing out lots of women.”

Mr James Jack, branch manager of Galbraith-Cochrane’s supermarket, coped with customers with one thought on their minds. “There is a great depression over the whole area – you can feel it and see it in their faces,” he said.

“You get to know people when you work in a supermarket – their faces at any rate – and today I’ve been looking around and wondering if any familiar faces are missing.”

The garage opposite the black area, flying its plastic bunting and news of free gift offers, has become the temporary refuge of the police and the other emergency workers, and also of reporters representing newspapers throughout Britain.

One cheering thing in these terrible days is the splendid help given by voluntary bodies and local women in Clarkston, who have rallied round to feed hundreds of rescue workers and anyone else who needs a cup of hot soup, tea, or a snack.

Mrs Pamela Birrell who with her neighbours Mrs Hamilton and Mrs Simpson and some other helpers, worked throughout Thursday night and yesterday.

Mrs Birrell said she and her husband had only moved to their house in Clarkson about six months ago.

“I don’t know anyone who was killed or injured but it doesn’t make the thing less painful to me. I’ve been too busy all day and night to cry but when I do get to bed I think I’ll cry myself to sleep thinking about it.

“Most women round here feel it could have been them. On Thursday at 3 o’clock I really should have been down at the shops with my little girl but fortunately for us, it wasn’t a normal day perhaps because of the weather.”

Mrs Birrell added, glancing down the street to the scene of the catastrophe, “I’m thinking just now that Clarkston will never be the same again.”