Cabinet Office - Justice and Security.
See also Part 1 (The government's case) of this series and Part 2 (Proposals and Consultation). Chapter 3 of the Green paper considers oversight of the services and how this might be changed. This should be read along with Appendix I to the green paper which offers a possible model for an Inspector-General.
Oversight of the Security Service and the Secret Intelligence Service is divided between the Intelligence and Security Committee (ISC) - which is a statutory committee of parliamentarians from both Houses - and the Commissioners: the Intelligence Services Commissioner (currently Sir Mark Waller) and the Interception of Communications Commissioner (currently Sir Paul Kennedy) - see Intelligence Commissioners website. The Green Paper Appendix G outlines the remit of the Commissioners and Appendix H the role of the Intelligence and Security Committee.
Oversight exists to improve the effectiveness of the bodies being overseen; detect