Editorial guidelines published by the BBC "set the standards" for the corporation, according to its website.
They are set by the BBC Board and also reflect the requirements of regulator Ofcom.
The BBC's Royal Charter outlines the BBC's mission, which is to "act in the public interest, serving all audiences through the provision of impartial, high‑quality and distinctive output and services which inform, educate and entertain".
BBC guidelines say employees must be aware of the contentious nature of any activity and take account of cultural and political differences between the regions.
The guidelines say that external activities which may give rise to a conflict of interest include public expressions of opinion, political activities and any involvement with charities and campaigns.