This afternoon or evening, Keir Starmer, the United Kingdom’s newest prime minister, will be briefed on its nuclear war plans and then pen a new “Letter of Last Resort” to the commander of each of its four Vanguard-class SSBNs, to be opened and read only if a nuclear war destroys the country.
Early in a crisis, two advance Central Government Exec Units (originally PYTHON Groups) would covertly disperse to 'safe' areas of the UK. Each capable of authorising nuclear release directly to the Trident boats. PYTHON, Northwood & London would have to be destroyed for the Letter to be opened.
A new prime minister reportedly has four basic choices (which may be combined) for instructing a ballistic missile submarine commander:
1. Retaliate
2. Do not retaliate
3. Put yourself under command of the US or Australian navy (if they still exist)
4. Use your own best judgment