Who gives way first?

[Glen]

Where the two right turn movements intersect, the traffic emerging from the side road passes in front of the give way marking, therefore traffic turning into the side road gives priority to that traffic flow from their right, in addition to the oncoming flow they are crossing.

The purpose is to create more opportunities for the traffic emerging from the side road to cross to the central reservation, as the right emerge manoeuvre at any junction is generally the highest risk.

[Chris5156]

Where the two right turn movements intersect, the traffic emerging from the side road passes in front of the give way marking, therefore traffic turning into the side road gives priority to that traffic flow from their right, in addition to the oncoming flow they are crossing.

This is like my very long post, but in one easy sentence

[FosseWay]

^^ It's also the same as my post earlier, which was also long, but without the very clear graphics that Chris used

TBH I don't think there's any doubt about what the markings mean, which is what I, Chris and Glen have all said. Whether that's what the highways authority intended is another matter. The other two questions it raises are:

(a) Is this (the specific road markings) the best way of telling drivers what they need to do? (Chris's question at the end of his long post)
(b) Is this (the whole idea of getting right turners off the A10 to give way to right turners onto the A10) the best solution in terms of safety and efficiency?

Personally, I think the answer to (a) is probably Yes. There is a clear Give Way sign, and the location of the markings leaves little doubt as to who has priority in the Triangle of Doom. But the road markings are very worn and should not be allowed to get in that state.

On (b) I have no idea. It depends on typical flows, and on how easy it is for people to turn right onto the main road there. Some uncertainty may be introduced by the behaviour of these right turners - they will either make the whole turn or stop in the central reservation to wait for eastbound traffic on the mainline. That will not necessarily be obvious to people turning right off the A10, as it depends on conditions behind them, which they're not necessarily looking at in the relevant circumstances. There is possibly a risk that, having stopped for someone emerging, they then start to move off under the presumption that the traffic crossing their bows will continue out of the way, when in reality it stops in front of them.

[Chris5156]

^^ It's also the same as my post earlier, which was also long, but without the very clear graphics that Chris used

I think I missed your post because it arrived while I was composing my illustrated monograph! I agree on all points.