The Mi5 seeks to protect the United Kingdom, its citizens and interests from internal and external threats while the Mi6 focuses exclusively on external threats. The Mi6 is officially known as the Secret Intelligence Service.
Differences between the two organizations extend beyond focus. They are answerable to different people. The Mi5 answers to the Home Secretary. This is an indirect confirmation of the organization's focus on domestic as well as external threats. In contrast, the Mi6 answers to the Foreign Secretary in part due to its exclusive focus on external threats. The two organizations have their headquarters in different locations. The Mi5 is based at Thames House. The offices of the Mi6 are located at Vauxhall Cross.
The budget and operations of the Mi6 are understandably cloaked in secrecy. In comparison, the Mi5 is relatively more transparent. In order to fulfill its mandate, the Mi5 concentrates its focus on several key areas. Terrorism, both domestic and foreign takes top spot on its list of priorities. This is partly due to the rise of global terrorism as a serious challenge to the security of the United Kingdom and its interests globally. To effectively respond to these threats, the organization is spending 65 percent of its 2014 budget on non-domestic counterterrorism. The rest of its budget is shared out almost equally between counterespionage and domestic terrorism. The Mi5 also works to counter subversion and the proliferation of weapons of mass destruction.