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I just knew as I typed it that someone would reply saying it must be someone's fault - at least you didn't disappoint me.
The accident happened when two cars passed my father in the outside lane of the motorway at high speed, causing his caravan to snake and quickly overturn. My father's caravan has an up-to-the-minute towing bracket, which thankfully absorbed the turn of the van otherwise the car would have gone as well, which doesn't bear thinking about.
The cars which passed were not speeding, so no fault there, nor were they too close. It was simply a combination of the air current from the passing cars, the tanker in front of my father and the lorry on the inside lane - no one's fault, just unlucky circumstances.
My mother would never sue my father, I can see where you're coming from, but their generation just doesn't think like that.
Any more ideas anyone?