THE SPIES WHO CAME IN FROM THE CONTINENT

From John le Carré’s novels to the insatiable popular interest in James Bond, Britain has long enjoyed, and cultivated, an image of producing superior spies. This reputation is based on more than myth. For decades during and following World War II, the painstaking real-world work of British intelligence officers was one of the United Kingdom’s primary sources of power.

That power, and its underlying foundations, is now in jeopardy thanks to Brexit, which will have a cascading series of repercussions for British intelligence: It will shut Britain out of European Union institutions that have benefited British national security, and it may also jeopardize the special intelligence relationship with the United States, which may look to deepen relations with Brussels instead. But while Brexit may now be inevitable, there are still ways for the U.K. to avoid this outcome.

Britain’s intelligence services—MI5, which handles domestic security intelligence; MI6, which does foreign intelligence; and GCHQ, which focuses on signals intelligence (SIGINT)—have been touted at home and abroad as the Rolls-Royces of intelligence