It has been argued in some quarters (e.g. CND Trident and International Law) that renewal of Trident would be a breach of the UK's nuclear disarmament obligations under the 1968 Non-Proliferation of Nuclear Weapons Treaty. CND argue that:
"The Geneva Convention Protocol from 1977 states that ‘the civilian population shall not be the object of attack’ and prohibits ‘methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment’. (See here)
It is impossible to use a nuclear weapon selectively, meaning that launching Trident would certainly be illegal as there would be a huge number of civilian casualties and devastation of the natural environment. The ensuing radioactive contamination of the area would also violate the population’s ‘right to a standard of living adequate for the health and well-being of himself and of his family’, as enshrined in the Universal Declaration of Human Rights."
A House of Commons Briefing Paper (SN06526 of 10th March 2015) has this to say:
"The UK’s Disarmament Obligations Article VI of the Nuclear Non-Proliferation Treaty commits the recognised nuclear weapon states to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a Treaty on general and complete disarmament under strict and effective international control”.
Successive Governments have insisted that replacing Trident is compatible with the UK’s obligations under the NPT, arguing that the treaty contains no prohibition on updating existing weapons systems and gives no explicit timeframe for nuclear disarmament. It also insists it has taken a number of steps in support of the NPT, pointing to the significant downsizing of the British nuclear arsenal since the end of the Cold War, with the withdrawal of all other nuclear weapons systems except for Trident, the reduction to fewer than 200 warheads in the overall stockpile and the reductions in the operational status of the deterrent.
Furthermore, the Government insists that sustainable nuclear disarmament can only be achieved through a multilateral process. The UK has the smallest nuclear arsenal of the five recognised nuclear powers and says it will be willing to place its remaining weapons on the table for negotiation when Russia and the US have reduced their arsenals to similar levels. Others believe the Government could do more to advance the cause of nuclear disarmament by reducing the UK arsenal further."
What is the position in international law?