I've been watching the crown (season 1) and the bit where Margaret can't marry a divorcee. Wasn't the CofE founded by Henry the 8th so he could divorce and remarry? Have I missed something or has the rules changed since then?
Henry had his marriage annulled, he was not divorced. Annulment has always been permitted in the Church of England, as it was in the Roman Catholic Church (and still is). The Papal objection for Henry getting an annulment was due to the Holy Roman Emperor being Katherine of Aragon's nephew.
However the rules have since changed in the Church of England anyway and divorced people can marry in Anglican churches. Individual clergy can decline due to matters of conscience but this is fairly uncommon (and the couple are provided with an alternative minister when this happens).