The car driver wasn't the only one who didn't follow the rules of the road.
The HGV remained for half a minute in what became lane 2 when the motorway became four lanes. The motorway rules say that the HGV should have moved into lane 1 at the earliest opportunity (i.e. drive on the left unless overtaking). We can see that lane 1 ahead of the HGV was clear for this purpose throughout the video (except for the car alongside him of which the HGV was clearly unaware). The HGV contributed to the collision as well. I'd say it was not being driven with due care and attention.
I heard it said that successful police driving is on the basis that the other driver is going to do something stupid. If both the car and HGV in the video had followed this principle, the collision would not have occurred.
I'm not claiming to be perfect by the way. I admit that I make mistakes too, we all do, but the important thing is to learn from each situation which is what we're doing by examining and discussing this incident here.
Simon