He then dashed up the road to where there was a single fire extinguisher, ran back and emptied it on the fire until it ran out. But the blaze raged on.
Only then did two marshals appear. Neither was properly clothed, equipped or trained.
Purley desperately shouted and waved at them to come and help him try to raise the car, but unprotected as they were they dared not come into the flames.
At race control, despite the huge cloud of black smoke engulfing that part of the track, there was no understanding of the severity of the accident, and the race went on.
Other marshals and a policeman arrived, but none of them could help Purley.
Despite being burned through his flameproof overalls and still wearing his crash helmet, he fought on desperately but fruitlessly to lift the car.
After eight minutes a small fire engine drove up but failed to put out the fire. Ten minutes after that a larger fire engine came to the scene, its crew wearing proper fireproof gear.
The fire was finally extinguished and the wreckage turned over. Williamson’s body remained in the cockpit and it was left to Purley to find a piece of cloth and cover his face.
Finally he walked away, rage and despair showing in every step.
Purley with his wife Jane outside Buckingham Palace in 1974 after receiving the George Medal for his bravery at Zandvoort
We know all this because the race was televised – the exception rather than the rule in those days – and the horrifying sequence was repeated on news bulletins around the world.
The following morning’s tabloids further dramatised the story by stating that Williamson and Purley were close friends.
In fact, they only knew each other as fellow competitors to nod to in the paddock, little more.
A day later David phoned me from Heathrow. He’d just landed, dodging the reporters as best he could, and before driving home to Bognor Regis he wanted to talk privately about what had happened, to try to get his head straight about it.
He came to my house in Chiswick, the burns up his arms heavily bandaged. I went out for fish and chips, and as we ate them in my sitting room David relived it all.
He had no memory of leaping from his car and running along the track, or grabbing the fire extinguisher: he said it was his army training kicking in, which taught him to take action at once if a fellow soldier was in danger.
Roger was apparently unhurt in the accident and was fully conscious, trapped in the fire, and David could hear his screams.
The ex-paratrooper had seen a lot; he was a tough guy. And yet, as he talked, tears filled his eyes.
They were not tears of sadness. They were tears of rage and frustration that something so disgraceful, so avoidable, had happened.