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Cars turning right from a minor road should give priority to the major road and to cars going straight or turning left from the minor road opposite. And so cars coming from the opposite side should give priority to you if you're turning left or going straight over should they wish to turn across you
No special rules for unmarked 4 way crossroads but all bets are off as to what the other people will do afaik -
From both sides. This is obvious if it's a narrow carriageway that allows only one vehicle to pass, irrespective of the manoeuvre you undertake.
If the main road is a two-lane road that's wide enough, you may be able to safely turn left while there is someone else coming from the left, but in general it's better to wait, because that person may want to turn right, too, which could put you into conflict. If you're turning right or going straight across, you of course have to give way to people coming from both sides. On multi-lane roads, a person approaching may want to change lanes, so again it's better to give way.
Driving, at a crossroad junction, the sign says Give Way. Should I give way to people from both sides, or just to my right like a roundabout?