In complex investigations, several different techniques will be used in combination, and much of the skill lies in deciding the most effective blend. Organisations which pose a threat to national security often go to considerable lengths to prevent and detect efforts to investigate their activities. The Security Service aims to gather intelligence while ensuring that the targets under investigation remain unaware of the Service's interest in them. Clearly there is a need to prevent the compromise of a potentially successful investigation while it is running, but the Service also needs to look to the future. Keeping secret the details of intelligence methods is important if the Service is to retain them for use in future intelligence operations.
Secrecy is also vital to ensure the safety of individuals, including agents.
The Security Service Act makes the Director General responsible for ensuring that there are effective arrangements within the Service to control the acquisition and disclosure of information. A major aspect of this control is a structure of internal mechanisms designed to ensure that the Service responds only to genuine threats, and does so with proper regard for the law, proportionately to the threat, and with appropriately senior authorisation for intrusive measures. These essential safeguards are also designed to allow fast-moving investigations to proceed swiftly, with proper authorisation, but without being hampered by unnecessary bureaucracy.