Executivedirectorsoforganizationsorpublic informationofficersare oftenthe mostaccurate and accessiblesources. Theyalsoshould be able to get youin touch with volunteersorothersources.
But if they have credible information of some risk to the public, officers can use powers of arrest and force - providing they use the minimum necessary in the circumstances.
Operation Elveden is looking at allegations that journalists made corrupt payments to public officials, including police officers, in return for information.