If your lane is blocked, move into the right hand lane. Continue in that lane until the left hand lane is no longer blocked and move back. Make sure you keep to the speed limit, don't get intimidated by other drivers being on your rear bumper. Don't stay in the right hand lane if the left hand lane is free, the right hand lane is for overtaking. Use your judgement, you should be able to tell where you need to be.
Definitely do not drive in the middle across two lanes, other road users won't have a clue what you are doing. Don't pull back into the left hand lane if 100 yards up the road it is blocked again forcing you to stop.
An examiner wants to see that you are confident on the road, and that you are spatially aware, and can plan your way through obstacles smoothly. They don't want to see you getting stuck somewhere because you were unsure if you were allowed to use a lane.