Set out that any leader and their government who deploys a nuclear weapon as an offensive measure or disproportionate response - anything other than retaliation under the principle of mutually assured destruction - should be refused UK entry, and diplomatic ties with them be severed. Retroactively.

Being the user or target of nuclear weapons represents a critically low point in our development as an (ostensibly) intelligent and ethical species. No matter where someone lives, they would be our neighbour if that bomb dropped on them; we would feel the moral/spiritual and scientific consequences. I believe anybody with that power and who acts recklessly with it, should not step foot on British soil or treat with us in a diplomatic capacity.