Not sure what a 50/50 call is?
I don't believe that UK ATC is anything other than impartial, but I do know some pilots don't agree! There used to be a war many years ago between two major British airlines at Heathrow - the only two airlines which engaged in such nonsense. Each thought the other was getting priority from ATC, but it was never thus. Controllers don't have time for this kind of thing, although I can't speak for those outside the UK.
I showed a foreign pilot around Heathrow once and he expressed amazement that we did not give BA priority!