Why does it have to be a conspiracy? Why can't it just be that certain referees favour certain clubs, or certain referees despise City?
Lahoz for one, never showed us any leniency or favour and always seemed to go against us. It's well rumoured that City had a dossier to show that one referee held a bias against us, and that referee was removed from City games before retiring to the USA. Also that City had a dossier of evidence to show that Raheem Sterling was unfairly treated by referees. Numerous referees have stated publicly that they favoured United, and there is evidence that United had influence in the selection of referees. (Winter never refereed United again, after having the audacity to dismiss Roy Keane).
There is no conspiracy needed here. It's just plainly evident that certain teams are favoured and certain teams are prejudiced against. Webb and his predecessors should not be appointing these biased referees in certain games.