One of the greatest dangers of our time is nuclear proliferation, particularly as we enter a more unstable international era. In a recent survey of 'the new world order' the Financial Times set out a series of bleak scenarios and concluded by quoting Gramsci writing in the late 1920s as Fascism emerged alongside Soviet Communism: 'The old is dying and the new cannot be born; in this interregnum, a great variety of morbid symptoms appear.'
It is worth reminding ourselves that the actual architecture of a nuclear bomb is now well understood, but to have a viable weapon you need:
1. A sufficient supply of weapons grade uranium or plutonium
2. The ability to miniaturize the weapon so that it could be used in a delivery device (the original French atomic weapon was said to be the size of a railway engine).
3. A delivery mechanism for the weapon: an intercontinental or intermediate range ballistic missile; a submarine launched missile (easier to escape detection); a cruise missile; an aircraft. (One could notionally have a bomb on a merchant vessel in an enemy's port, but I don't rate these scenarios as very likely).
4. A robust launch mechanism (I certainly have doubts about the UK's launch mechanism in so far as it is in the public domain, but that information may be dated or there may be back up procedures). However, each new prime minister is required to write a letter to each commander of a submarine able to fire Trident about what they should do if the UK appears to have been attacked, (see below).
The two principal nuclear powers are the United States and Russia and, even with reductions, they have enough weapons to destroy each other several times over as well as plunging the rest of the world into a nuclear winter.
China had a relatively small number of weapons recently, enough to make a potential aggressor to think twice like the French 'force de frappe'. They are now engaged in a rapid catch up with what strategic objective in mind is uncertain.
India and Pakistan have enough weapons to inflict considerable damage on each other. It is believed that the US has provided them with sophisticated command and control mechanisms to prevent accidental discharge. North Korea has now become a serious nuclear power and a recent work of fiction outlines a world war it starts more or less by accident (although the scenario has been questioned). The domino effect is shown by the fact that there is now a debate in South Korea about developing nuclear weapons.
Israel has long been assumed to have nuclear weapons, although it has never admitted their presence. According to some reports, Iran could develop a viable device within a short time frame.
South Africa developed nuclear weapons and was preparing a test, but dismantled its weapons after the fall of the apartheid government and became the first former nuclear power to sign the prohibitions treaty. (There is some dispute whether South Africa did carry out a test, possibly in collaboration with Israel). Brazil ruled out their development. Countries like Saudi Arabia could develop a weapon if they so decided.
Anyway there are enough nuclear weapons in enough countries to give cause for concern.
The letter of last resort
Each incoming UK prime minister is required on taking office to write a handwritten letter to each of the missile firing submarine commanders advising them what to do if the UK and its government is wiped out in a nuclear attack, established by whether Radio 4 has ceased broadcasting. No one knows what is in these letters and it is not true that Liz Truss wrote 'Destroy the blob!'
My letter would say [bearing in mind that the boats are most likely to be in the North Atlantic]: 'Do not fire your missiles. Do not return to the UK whatever the crew wants. Proceed to the British overseas territory of St. Helena, surface, re-supply and establish what has happened, whether you can be of any use in the UK, or otherwise proceed to an Australian port.'