David Shayler, a former MI5 officer who served from October 1991 to October 1996, disclosed secret documents to The Mail on Sunday in August 1997. The material alleged that MI5’s counter-subversion branch had monitored left-wing groups and vetted Labour politicians, including Peter Mandelson, Jack Straw, and Harriet Harman. Shayler also alleged that British intelligence had prior knowledge of terrorist attacks and had planted or manipulated stories through journalists. These claims were contested and were not established as fact by the courts.
Shayler separately alleged that MI6 funded a failed 1996 plot to kill Libyan leader Muammar Gaddafi, involving a £100,000 payment to the Libyan Islamic Fighting Group; the source says the bombing struck the wrong vehicle and killed civilians, but does not provide an independent official finding confirming the allegation. After returning to Britain in August 2000, Shayler was charged with three breaches of the Official Secrets Act 1989. He represented himself, arguing that public-interest disclosures should be protected, but the court rejected that defense. Convicted in 2002, he served six months in prison with time on remand counted, highlighting the limited legal protection then available to intelligence whistleblowers.