The history of MI5

MI5 has existed, in different forms, since 1909. We are unrecognisable now when compared to our earliest days in a rented building where the two employees who made up the Secret Service Bureau worked. 

Where it would not be to the detriment of national security to do so, we release files to The National Archives so that others can explore our history and draw their own conclusions about what we have done over more than a century. 

There is much in our history that we are proud of, where we have worked innovatively together as a team to protect the UK from threats to national security. 

There are also some episodes and practices which do not reflect the organisation we are today. It is important to us that we share as much as we can to explain what we do, and how we do it. These pages contain some information about our history as well as details about how to find out more.