Hi chaps! newbie here ! Not been driving class 1 for long, and I hope you guys can give me a bit of advice on how many lanes and the best road positioning to turn left or right at roundabouts. I have been approaching certain islands with a 2 lane approach, and when I get to the island I find that I need 2 lanes to make my turn and there are cars already in that lane. when I was taking my lessons , the instructor knew all the roads, islands, etc, etc, and how many lanes that were needed at certain locations, but now im on my tod and seeing roads for the first time it can get a bit hairy at times ! I try to read the road ahead as far ahead as possible and also I try to look ahead to see how other hgvs manouvre around islands, so I can do the same, but sometimes for example, I want to turn right at a island, the left hand lane is queuing of traffic and the right hand lane is clear so you go down that lane, then you find when you get to the island you need 2 lanes! (The ring road around Norwich is a classic example!)
Welcome aboard Pat. 
I would suggest you straddle the lanes if you have any doubt you need more space than you have with one lane.
It’s not being bolshy, it is taking control of the situation. You are far better off taking up a little more room than you need than getting onto a roundabout and getting stuck because you have allowed a car to get where you need your trailer to be.
Remember most car drivers don’t have an LGV licence, so you must take control and stop them getting into a position where they are in danger of being hit.
After a while, you will be surprised at how accurately you can judge whether or not one lane is enough. 
Hi Postman Pat.
I basically agree with what Flying Fenman said, but it really just comes with experience.
As for roundabouts on the norwich ring road I know them well and many are easier of you take both lane on the entrance to them. Especially the Newmarket road A11 one coming from Dereham road direction. I’ve seen plenty of truck on the kerbs because they didn’t.
Or and the Dereham road one, and the Wroxham road, and Hall road, County Hall not to bad, but a real nightmare if you are trying to get out of Britvic. North Walsham road quite wide, but it’s not round. 
Five ways at Heartease take all lanes which ever way you are going, 
yep good answers by them two guys, it is all about controlling the situation because car drivers are never sure where your going,and don’t forget the indicator. when you do that keep checking your mirrors for the biker/cyclist who doesn’t think anyone should be on the road except them.
Hi again chaps! Thanks all for the good advice, there is just 1 thing im still unsure of, and that is how far of the island do I take 2 lanes up if I think I will need them at the island? I am asking this, because I have took 2 lanes up and there were about 20 cars in front of me. Because it was rush hour traffic, cars were overtaking me because they could see the right hand lane was free and there was quite a good distance between myself and the island, because I had decided to take 2 lanes at the earliest opportunity. Was I correct in doing this? Or would it have been better to go down the less busy right hand lane, indicated left when I was nearer the island, and then had 2 lanes?? 
Just take control when you can and need to. theres no set rule for distance but give yourself enough time to get in the right position
postman pat:
Or would it have been better to go down the less busy right hand lane, indicated left when I was nearer the island, and then had 2 lanes??
No, cos you’d find cars sneaking up your inside, in your blind spot, and not letting you in!!
If you need both lanes at a roundabout straddle the line and block cars from using both - the sensible ones will realise what you’re doing and hang back to give you room - idiots ones might not
If that happens to me i just let them get by, but if they do it just before or while going round the roundabout just hit them. As stupid as it sounds you have doen everything in you power to warn other users by straddling both lanes and by indication of direction if the impatient ones wont waiti personaly have no problems what so ever in sending them up the roundabout pooing there knickers, its there own fault for trying to jump ahead with out consideration for others.
After a while you will be able to judge from a distance how to approach each roundabout. In the meantime prevention is always better than cure and you are going about it the right way.
Discard the first paragraph until you feel experienced enough to do it