5. The family is not allowed to publicly discuss or hold political opinions.

Reason: They must be independent of politics.
Humanitarian causes (banning landmines, for example) are an exception.
The Royal Family is supposed to remain above politics, as this list makes clear; hence, they do not cast ballots. These heads of state are required to maintain their impartiality on all political issues, so they avoid getting bogged down in the mud with the MPs.

The family is not allowed to publicly discuss or have political opinions. ©Think Tank/Getty Images
The Royal Family may support non-debatable general humanitarian causes, but they are not permitted to express their political views on tax legislation, urgent matters, or scandals. The media has frequently exhausted itself speculating about the Royal family’s political stance, to little use.