There is what the highway code says should be done, then there is what is actually done.
That roundabout is a complete pig, it's busy, got a load of roads coming onto and off of it, and is actually quite narrow, with that paving around it that most people seem to be scared of driving on.
I tend to barge my way round it in, but from where you have indicated (hulbert road, which isn't actually dual carrigeway, just splits where it joins the roundabout so there is a seperate entrance and exit) if I was the red car then I would go to exit 2 and 3, and then for the rest use the right hand lane, which is what most people do.
If you are in the left lane, and hoe to go to 4, then you will get 3 or 4 idiots pulling out in front of you from 4.
So, the above is reality, which is probably completely different to how you should theoretically go round that roundabout.