Scottish CND     magazine
.. the threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law. (para 2E)
..states must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets. (para 78)
The Geneva Convention Protocol 1977 prohibits attacks on civilians and methods of warfare which are intended, or may be anticipated to cause widespread, long-term and severe damage to the natural environment. (Article 35)
On these grounds Trident is illegal.
Scottish CND      magazine