Thats the underneath of a banger you're seeing Andy.
But the car in front that you thought had a barrel in it, got loaded up cos he had a fire extinguisher based petrol tank with the feed, breather and return pipes loosely siliconed in to the tank and was leaking when it rolled.
The car that went up in flames had the original tank and fuel injection. The tank cracked and also the fuel feed popped off at the engine. The driver baled out with the ignition (still on the key and with dash in place) still on. So the fuel pump was still spurting out fuel onto the hot exhaust. After emptying 5 or 6 extinguishers only for the blaze to start again, it took one of us to jump into the blazing car and turn the key off to get the fire to stop, because Crimond don't require a cut off switch! That's my head you can see behind the number fin in the pic of the fire and I'm still coughing up extinguisher powder yet!!