Sometime soon after entering Downing Street as prime minister, Keir Starmer will be briefed on the deadly capability of Britain’s nuclear deterrent – and asked to consider what instructions to give Trident submarine commanders in the unlikely event the UK is destroyed in an all-out attack and he is among the millions killed.
In the aftermath of an election victory, it is a sobering moment. Tony Blair is described as having gone “quite quiet” just over a quarter of a century ago when asked to handwrite four identical “letters of last resort” to the commanders in the event that the UK no longer in effect exists.
James Strong, a senior lecturer at Queen Mary, University of London, said the exercise acted as a counterweight to the drama of staying up all night, winning an election and visiting the monarch. “This is the moment where prime ministers say the reality of the job dawns on them, and that may be a reason why it keeps being done in this way”.
Although the scenario of a full-scale nuclear war is vanishingly unlikely – recent events suggest a highly deadly pandemic is more possible – Strong argues “it is a ritual where you are being inducted into this separate level, almost like a coronation” where the prime minister becomes commander in chief.
While the previous Labour leader Jeremy Corbyn was personally opposed to Trident, Starmer has already signalled he supports it – and would if necessary fire nuclear missiles. “We have to be prepared” to unleash the deterrent’s destructive power, the new prime minister said last month, describing it as “a vital part of our defence.”
The briefing is led by Adm Tony Radakin, the head of the armed forces, accompanied by what one former Downing Street official described as “stern-faced admirals in improbably grey suits”.
There are about 40 warheads on every Vanguard submarine that carries the Trident missiles, though the exact number is a secret and may be slightly higher. Each is estimated to have an explosive power of 100 kilotons, according to David Cullen of the Nuclear Information Service – theoretically powerful enough to cause serious blast damage in a 3km radius.
In a time of war, it would fall to the prime minister (or if he or she were unavailable or dead, a nominated alternative whose identity is not disclosed) to authorise a nuclear attack.
The letters to the four commanders are handwritten, not necessarily immediately but relatively promptly. There are considered to be four basic options: retaliate; do nothing; join forces with an allied nation, probably the US; and even leave the matter to the commander’s discretion. “Taking the last option really would be passing the buck,” Strong said.
Once written, the letters are sealed in an envelope, and can only be delivered physically. Soon after, they are deposited in what one former Trident commander described as a “safe within a safe” in each of the submarines. There has been a British nuclear-armed submarine at sea on patrol at all times since 1969.
Meanwhile, Sunak’s instructions to the submarine on patrol remain in force, until a new boat has gone out with one of Starmer’s letters. Once no longer needed, the old prime minister’s instructions are destroyed, and what they have said has never been publicly disclosed, to maintain an aura of uncertainty.
Navy insiders say a complex verification process exists before a letter can be opened, which requires determining whether the UK has been subject to an all-out nuclear attack. That involves listening for signals from home – which back in the 1960s could only come from Radio 4 and other longwave radio stations – but today comes from a wide variety of sources, including mobile phones, GPS and shipping radio.
It is also likely there would be world news, listened to at sea, describing a dramatic escalation of global tensions. “You might expect that the level of ‘proof’ which the commanding officer would be required to amass before opening the PM’s letter to be extremely high, and so it is,” one former navy submarine commander said.
