The Second World War ended with Europe divided between the two superpowers, the United States and the Soviet Union. Subversion and Soviet espionage were key concerns during the Cold War, and from the 1970s onwards terrorism also emerged as a serious threat to national security.

• Bad Nenndorf

The story behind the 1947 controversy at a British interrogation centre in Germany

• The British Empire and Commonwealth

How MI5 worked to ensure the security of the late British Empire and the early Commonwealth

• Klaus Fuchs

How one of the Soviet Union's most valuable spies in the UK was exposed by MI5. Includes copies of original documents from the MI5 case files.

• The later Cold War

MI5's work against Soviet, Eastern Bloc and Chinese espionage against the UK in the later part of the Cold War, and the rise of terrorism in Northern Ireland during the Troubles

• The 'Wilson Plot'

Did the Security Service spy on Harold Wilson? The facts behind the long-running controversy

• The threat of subversion

How MI5 responded to fears that communist and Trotskyist groups were infiltrating British trade unions and political parties