Now Keir Starmer Has to Decide if He’d Use Nukes

Following a landslide victory for the Labour Party, Britain has a new leader. The moment Keir Starmer is officially made prime minister of the United Kingdom, he will be given a flurry of briefings, piles of documents, and the urgent business to run the country. Lurking among those papers is a moral land mine.

Starmer will be given a pen and four pieces of paper. On each paper, he must handwrite identical top-secret orders that—hopefully—no other human being will ever see. The previous set of orders, written by outgoing Prime Minister Rishi Sunak, will then be destroyed, unopened. These top-secret papers are called the “letters of last resort.”

Since 1969, Britain’s nuclear deterrent has operated at sea, with nuclear missiles that could be launched from at least one continuously deployed submarine. Destroying those vessels would eliminate the United Kingdom’s nuclear deterrent, so the secrecy of the patrolling submarine’s location is paramount. Once deployed, the submarine may not transmit messages, only receive them, to maintain its crucial cloak of concealment.

Today, there are four submarines—one always on patrol—which is why there are four identical copies of the letters. Each handwritten letter is placed inside a safe, which is housed inside another safe, on board the nuclear-armed submarine. Right now, one of those submarines is patrolling the world’s oceans, its location known only to a tiny number of people at the highest levels of the British government.

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During the Cold War, British authorities constantly feared that London could be wiped out in a surprise nuclear attack by the Soviet Union. If the British government ceased to exist in a blinding flash of atomic light, and everyone in the civilian chain of command was dead, who would have the authority to launch a counterattack? Without the credible threat of a “second strike” in response to a nuclear assault on the capital, Britain lacked a deterrent.

The letters of last resort are the solution to that dilemma: They allow the prime minister to issue orders for a counterattack from beyond the grave. If the submarine captain has reason to believe that London has been destroyed in a nuclear blast (one of the cues is said to be that the BBC has stopped broadcasting), then the captain is to make every attempt to verify that the British government no longer exists. Once satisfied that the worst has indeed taken place, only then may the captain open the two safes, unseal the letters, read their contents, and execute the order from the now-deceased prime minister. Should the United Kingdom release its nuclear arsenal and retaliate—or not?

The briefings with the prime minister are secret, but four main options are typically presented to the incoming leader: retaliate, don’t retaliate, put the submarine under the control of the United States Navy, or leave it to the commander of the submarine to decide. Because it’s impossible to forecast what has occurred, the letters must be elastic enough to respond to the annihilation of the British government, whether caused by Russia, North Korea, or a rogue terrorist group that has somehow acquired weapons of mass destruction. There is just one letter per submarine.

“The prime minister can write on that piece of paper anything that he likes,” Robin Butler (also known as the Right Honourable Lord Butler of Brockwell) told me when I met him in his flat in Westminster a few years ago. He had served as the private secretary to five prime ministers, briefing the newly elected ones on the responsibilities they’d assumed. During the Cold War, the very existence of the letters was top secret—nobody outside the highest echelons of the British government knew of them—so the need to draft them came as a shock to incoming prime ministers still riding the euphoria of being elected. Even though the letters are not a secret today, writing them is still daunting. A new prime minister must decide whether he or she is willing to engage in nuclear warfare. (Liz Truss may have failed to outlast a lettuce, but she did decide whether she would use nuclear weapons.)

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After explaining the protocols, Lord Butler would tell incoming prime ministers to write down what they had decided. “All I did was to leave successive prime ministers with a piece of paper and a pen to write out what those instructions should be,” Butler told me. “But it must be, above everything else, the thing that brings home to them what the weight of their responsibility is.” Britain has, by accident, designed a protocol ensuring that new prime ministers cannot come to office thinking only of themselves, but must contend psychologically with the burden of power, too.

If the worst were to happen, the letter on board the patrolling submarine would be opened. If the prime minister had given orders to retaliate, the crew would immediately fire as many as eight Trident missiles comprising up to 40 warheads, with a payload that would make the Hiroshima blast look comparatively minor. The trigger mechanism incorporates a handle from a modified Colt 45 revolver. (The training trigger is black, whereas the real one is red.) It will operate only when the captain has turned a key to the “Fire” position, ensuring that two people are required to initiate a launch.

This weekend, Keir Starmer, like all prime ministers for the past five decades before him, will write his orders for what to do if the British government is wiped out. Unlike American presidents, who must only contemplate the terrifying nuclear power they control, British prime ministers must actually decide—definitively—whether they would use that power.

Prime ministers are hesitant to discuss the letters of last resort, and none of the handwritten orders has ever been seen. That’s understandable, because if the letters included any orders other than for a full-blown second strike, Britain’s adversaries would know that, and it could heighten the risk of a nuclear attack.

Nonetheless, former British Prime Minister Tony Blair spoke with me in 2020 about the letters of last resort. On taking office in 1997, Blair told me, “Whereas everyone else was euphoric, I really wasn’t. I was oppressed by the weight of the responsibility that was descending upon me and very conscious of it—very conscious of the fact that campaigning for office and governing in office are two very different things.”

The letters themselves didn’t weigh that heavily on Blair, however, because he took power during a period of comparative peace and prosperity, when the prospect of nuclear war seemed far-fetched. “Yes, of course, I paid a lot of attention deciding how I drafted the letters,” he said. “But it didn’t seem to be anything other than an extraordinarily remote possibility, so I can’t say it occupied my thoughts greatly.”

The same is unlikely to be true for Starmer, who takes office at a moment of global peril. Russia’s invasion of Ukraine has raised concerns that nuclear weapons could again be used in warfare. North Korea’s eccentric dictator continues to test his arsenal. Iran is more openly flirting with acquiring nuclear bombs. And one of the options prime ministers usually consider—turning over Britain’s nuclear arsenal to the United States Navy—could soon mean putting even more nuclear firepower in the hands of Donald Trump.

If the letters are opened, and they call for the awesome power of Britain’s nuclear arsenal to be unleashed, a deafening sound will follow—of missiles traveling at 18,000 miles an hour before exploding in a cacophony of death. This weekend, Keir Starmer must contemplate the destructive capability he now wields, while listening to a much quieter sound: the scratches of his pen on four pieces of paper that could determine the future of humanity.