Difficult to answer without more information because it depends on the Councillors connection with the particular outside body. If the outside body is a Company then it will be subject to company law and can be sued , and if the Councillor was appointed to a committee of the company then that may cause problems . Similarly , Charities are governed by charity laws and code of conduct which are similar to the Nolan principles. I would say that generally it would make sense to abide by codes of conduct so long as they do not contravene the Nolan principles.