100% the cars fault. You can see the HGV indicator flashing ages back so his intentions are obvious.
is a crash from 2018 still being disputed?
I've replayed it a few times and really struggling to see the indicator. Possibly for 1 frame, but not a regular flash.
If it was indicating then car's fault, but in all honesty, I could imagine myself doing the same, if the indicators are as barely visible as the video suggests. Before the horsebox moves right you can see a layby/turn the opposite side of the road, so I really thought it was going to head that way, just turned quite early.
I don't think either are innocent and I could imagine it possibly being argued to 50/50 by either side.
I'm suprised by that! Good to know the answer.

He drove in to the back of a horse box. Drivers fault. Yes the van was in the middle of the road before turning left without signals, but being in the middle of the road should have been enough for the car driver to hang back and not try to undertake.
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Who's fault would you say the blame lies
I don't get what the driver was doing driving past like that. What did they think the horsebox was doing pulling out to the oncoming lane?
Wasn't immediately clear what the horsebox is doing on the right of the road with no signalling.
Horsebox 90% - the horsebox was not indicating
100% horsebox as he hasn't just swung wide he has re-entered the carriageway (lane) and should have stopped, indicated and checked it was clear.