Accident on a road bend - who's fault is it?

Hi,

One of my friend was on the right most lane of a 3 lane road of which the left most lane goes straight, the right most lane bends and turns right while the middle lane can be used to go straight or trun right. just 15 yards from the bend he realised that he should be in the middle lane as he was suppossed to go straight and put on his left indicator to move into the middle lane. He said he checked his left and rear view mirror to see if there are any cars on his left coming on the middle lane. He also said that he was doing around 20mph and was slowing down to swap lanes when a car rushed on from his left (about 10 yards from the bend) and hit his front left bumper and the side wing. He said the other person might have been doing well over 30mph (on a 30mph road) and went a few yards after the collision before stopping.

The other person started blaming my friend saying he was at wrong as he was in the wrong lane. But my friend did put on his indicator and started moving into the correct lane when this guy hit him plus he was speeding.

Could someone tell me who is at fault in this case.