MI5 handles security inside the UK; MI6 handles intelligence outside the UK.

Simple difference (ELI5 style)

Think of it like this:

  • MI5 = “home” spies
  • MI6 = “abroad” spies

MI5 focuses on threats within the UK’s borders (like terrorism, espionage or sabotage happening in Britain), working closely with police and other domestic agencies.

MI6, officially the Secret Intelligence Service (SIS), focuses on gathering foreign intelligence and running covert operations overseas to spot and counter threats before they reach the UK.

What MI5 does

  • Looks at domestic terrorism and radicalisation inside the UK.
  • Counters espionage by hostile states or groups operating in the UK.
  • Protects key infrastructure and supports cyber‑security at home.
  • Works with police and other agencies but does not itself arrest people; it provides intelligence so others can act.

An example often cited is MI5’s role in disrupting terrorist plots around major UK events such as the London Olympics, working largely behind the scenes with domestic partners.

What MI6 does

  • Collects intelligence overseas about foreign governments, terrorist networks and criminal organisations.
  • Runs covert operations and human intelligence networks abroad.
  • Works closely with foreign partners such as other national intelligence services.
  • Supports UK foreign policy, defence planning and crisis decision‑making with intelligence from outside the country.

Historically, MI6 has been involved in wartime and Cold War espionage, as well as modern operations against international terrorism and cyber threats that originate abroad.

How they work together

  • A terror plot with links overseas might involve MI5 tracking suspects and networks inside the UK while MI6 follows their contacts, funding or training camps abroad.
  • They share intelligence so the government has a joined‑up picture of both domestic and foreign aspects of a threat.

In short: MI5 protects the “home front”; MI6 ranges “overseas” to spot and shape threats before they arrive.

Information gathered from public forums or data available on the internet and portrayed here.