IIRC, it was only if there were no give way or stop signs and the roads didn't have centre lines, so the 'give way to the right when turning right' would apply - I would treat it as the vehicle on the through road had priority and, TBH, as far as I recall, so did everyone else.
However, I used to do a lot of trials in the local car clubs and they had a defined way of establishing road priorities.