Minor road - long straight hill
Parked cars on either side so only room for single flow of traffic but with gaps to use as passing places
Who has right of way/ priority ? - Cars coming up hill or cars going down hill.
Cant see anything in Highway Code ?
I would say common sense and some courtesy would go a long way on this one it would also depend on the size of the vehicles involved and the size of the passing places,i would think that if someone is already passing the parked vehicles as you come to them or visa versa then they/you would as you wouldnt be able to pass any way if there wasnt enough room for both parties,if no one has,or both arrive together try and time it so that you or they can get into one of the passing places,if it is a larger vehicle hgv etc i would tend to let them go wether up or down the hill as it is easier to stop and pull in in a car,i know in reality you will always get the one thats going to go wether you like it or not,but just let emm go their not worth it,
only my humble opinion of course,