For some roles within the Security Service, like foreign language analyst or security guard, you would not need any specific qualifications. Entry would be based on the experience and skills you could bring to the role, for instance fluency in a language like Russian or Mandarin.
There could also be opportunities for you if you have technical, vocational or professional qualifications in subjects like electronics or accountancy.
For support jobs such as business officer or administration assistant, you may need five GCSEs at grades 9 to 4 (A* to C) or equivalent including English and maths, or have relevant office-based experience.