This is getting boring. Yes, you give way to ALL lanes. Most don't do it, I agree that it doesn't work in busy cities, but nevertheless it is the law, and one which you have proven without a shadow of a doubt that you are completely ignorant of.
I reckon you are missing something fundamental here, and that is what 'give way' actually means.
"slow down and, if necessary, stop to avoid a collision."
The rule that you have to give way to any vehicle already in the roundabout means that you slow down and stop if necessary to avoid a collision with any vehicle already in the roundabout. It most definitely does not mean you can't enter the roundabout just because there are other vehicles in it, in lanes and/or positions that don't present a chance of a collision.
When a vehicle is turning right in the middle lane, and you are turning left or going straight through in the outer lane, you can enter the roundabout if it's clear doing so isn't going to cause a collision. Once you've safely entered the roundabout, the other driver has to comply with the requirement to give way to any vehicle in the lane he's attempting to change into.
Where it becomes tricky is when the right turning driver starts changing lanes at the same time the other driver is entering the roundabout, although that right turning driver should be indicating left prior to changing lanes, which would alert the other driver to the fact than entering the roundabout could cause a collision.
As I said yesterday, I'm not convinced this is as clear cut as you keep suggesting, but I'm happy for you to correct me if you can point out an error in my logic.