is that not for cases where the car is already in your lane? I don’t know how it can be applied to cars who spin into your lane as how can you leave a stopping distance for them?

If he set himself into a spin by a late/violent manoeuvre to avoid a van, and he's already accepted responsibility for that, then I think he'll struggle to avoid being held liable for impact with you too.

You have dashcam footage which should give a reasonable account of whether you were too fast for conditions or failed to brake in time.

To me, it appears that the OP was in the outer lane while the accident was in the inner lane. No reason to think that they might have been 'following too close behind'.

Did the parked van have its lights on. If so it could be argued that you should have seen the van and the car and perhaps anticipated a car pulling out in front of you. Driving at night in poor conditions is something I do not like, For the car to hit the stationary van and spin out in front of you the driver must have lost concentration, have poor eye site or going too fast. I think that you would have priority in the outside lane and the driver who caused the accident should have slowed to let you complete the overtake. You are at fault these days just by being there!!! At night on a dual carriageway overtaking is always more stressful especially on unlit roads and greater care is needed.