Green Lanes / Alfoxton / Frobisher junction

tl;dr: I use this junction most days, so probably have too much to say about it. Even if there is a clear rule that applies, behavior suggests large numbers of people aren't aware of what it is and I remember it being a bit of a mindf*** the first time I drove it 10 years ago. Perhaps a rethink is in order?

Returning from yet another trip having to navigate this junction and having had a close call, I wanted to get opinions on what the actual rule is for priority at this junction.

To me it is not 100% clear, but based on behavior I feel it is clear to some others. Crucially, what is clear to others seems to differ in a way that puts them in conflict and I do wonder how insurers would rule in the event of an accident!

At this junction, turning North into Green Lanes from either Frobisher road (left turn, from a slip lane) or Alfoxton Avenue (right turn, from a slip lane) both get a green light at the same time. 

Here's the streetview view, from Alfoxton Avenue : 

https://www.google.co.uk/maps/@51.5872774,-0.1010288,3a,75y,241.43h...!3m6!1e1!3m4!1sBEoCpBEPwU-6tF_AXvY3ag!2e0!7i13312!8i6656

Here's what I've seen as possible rules/assumptions/behaviors/options 

1. Vehicles coming from Frobisher road have priority. They are turning left. Vehicles turning left into a road have priority over vehicles turning right into a road. In this version, this is true even for vehicles coming from Frobisher Road and going directly into the right hand of the 2 northbound lanes on green lanes. If you don't follow this rule when coming from Frobisher, expect honking from people behind you who subscribe to this option. Whilst I think this is the most likely rule to apply in the event of a collision, it seems rare that all the vehicles from Alfoxton wait for all the vehicles from Frobisher.

2. There is no conflict. There are 2 lanes on green lanes at this point, so vehicles from Frobisher join the left, vehicles from Alfoxton join the right. Change lanes as usual along Green Lanes as required (vehicles from Frobisher will frequently want to move right to turn into West Green Road). Following this option is quite high risk, due to vehicles subscribing to option 1 or 4 and also you need to watch out for any larger vehicles that need both lanes to make the turn. Finally, the lanes aren't actually marked directly on the junction.

3. Noone has priority, so merge in turn. Probably achieves the highest throughput but I can't think of any basis for it other than courtesy. It does seem to happen smoothly like this a lot. It's probably the safest too as you can just hold back if someone's thinking another one of the options is the right one. 

4. Vehicles coming from Alfoxton Avenue have priority because...nope...I've got no idea why they would have priority aside from the possibility in option 2 where they go into the right hand lane. I include it though as it seems to be what happens the most, probably because it is the A road in the set-up and carries the most traffic. Some people go directly into the left lane from Alfoxton cutting across people emerging from Frobisher. I guess they either don't know the lights are both green or they're simply road hogs. If you're coming from Alfoxton and don't follow this rule, or at least attempt to merge or barge your way in at some point, expect to be beeped from behind.

I used to go with option 1 when coming from either way, but had some close calls with people following option 4 when coming from Frobisher and much beeping from people behind when coming from Alfoxton. So now usually I follow option 3 and merge in turn, but also try to keep to the side of the road I'm coming from like in option 2. This mostly gets me through clear, but this afternoon I was coming out of Alfoxton and heading into the right hand lane in green lanes - I waited for the first car from Frobisher but hadn't properly clocked that the taxi behind them was following them very closely. So we ended up side by side (ie. option 2), but he wasn't happy about it!

If anyone thinks they can provide a definitive answer, it would be useful to know whether it's a professional opinion (eg. police, driving instructor, insurance loss adjuster!). Me, I'm just trying to get around London without dents.