Car went into the side of mine in a dual carrageway?

I was in the right lane and he was in the left on a dual carrageway just approaching a junction to my right he proceeding to come into my lane ( i was about half a car lenght in front of him) half my drivers door is all scd, the bottom of the car where you put you feet to climb on, and the only damage to his car is his wheel arch. when we stopped he told me he wanted to take the right junction turn, for which i told him he had to be in the right lane to do that and not cut across traffic going straight on. can anyone confirm to me that he is at fault.