If you were exiting roundabout into the inside lane of dual carriageway, your fault.

If you were exiting roundabout into the outside lane of dual carriageway, his fault.

You're meant to maintain your lane if entering a roundabout on a dual lane junction, you should exit in the same lane. So, enter on outside, take roundabout on inside, exit roundabout on outside and vice versa.


Cheers,
Grant