score:4
I think that traffic going W->S has priority over traffic going N->W.
The logic behind it goes: As you approach from the west, you have a give way line. You therefore have to give way to traffic on the main road (S->N). As the other car approaches from the north, he too has a give way line - but his line faces onto the turning right lane, not onto the main carriageway - therefore he has to give way to traffic in that lane, i.e. you.
Either way I'd always treat it with extreme caution, watching both the main road traffic and the crossing traffic. I've seen some very close calls there, including having to take avoiding action myself about 10 years ago when a car going W->S pulled straight out in front of me as I was heading down the main road N->S...