Who would be at fault if two vehicles change to the same lane and collide?

What would happen if the above video ended in two vehicles colliding? From the video you can see I’ve started to change lane before the other driver even indicates, it’s only a matter of milliseconds but if you look at the position the van is facing you’ll see it’s changed from straight on, to a little to the left. The rules of the road state you must give way to somebody who is completing a turn or maneuver so I’d say I’d be in the clear, but it’s a close call and I’m not sure if everyone, in particular an insurance assessor, would see it the same way?

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