R (A) v B  EWHC 2361 (Admin)
"The police are under an absolute and unconditional obligation to take all steps which appear to them to be necessary for keeping the peace, for preventing crime or for protecting property from criminal injury. ... Article 8 ... provides that: '1. Everyone has the right to respect for his private and family life, his home and his correspondence. ...' This case concerns the interaction of those two principles in a situation where the police believe that a citizen, though committing no crime and though free of any criminal record or allegation of crime against him, has engaged in a private sexual life which indicates he may become a danger to women and propose to make public the details of this by selective disclosure."