When approaching a roundabout, you must give sufficent warning to other road users of your intention to turn left or right by indicating as you approach the roundabout.
When exiting a roundabout, whether you are turning left, right or even going straight ahead, you must always indicate a left turn just before you exit, unless it is not practical to do so.
Turning left
If there are multiple lanes you must approach in the left lane and stay in that lane. You must indicate a left turn on your approach to the roundabout and keep the indicator on until you have left the roundabout.
Turning right
If there are multiple lanes you must approach the roundabout in the right lane and stay in that lane. You must indicate a right turn on your approach, and indicate left, if practicable, just before the exit you are turning into, keeping the indicator on until you have left the roundabout.