“No court may require a person to disclose, nor is any person guilty of contempt of court for refusing to disclose, the source of information contained in a publication for which he is responsible, unless it be established to the satisfaction of the court that disclosure is necessary in the interests of justice or national security or for the prevention of disorder or crime.”
“… like many other questions of fact, such as the question whether somebody has acted reasonably in given circumstances, it will call for the exercise of a discriminating and sometimes difficult value judgment. In estimating the weight to be attached to the importance of disclosure in the interests of justice on the one hand and that of protection from disclosure in pursuance of the policy which underlies section 10 on the other hand, many factors will be relevant on both sides of the scale”