The 100-page Integrated Review document sets out the UK’s national security and foreign policy approach.  The following is an excerpt from the document.

“The fundamental purpose of our nuclear weapons is to preserve peace, prevent coercion
and deter aggression. A minimum, credible, independent nuclear deterrent, assigned
to the defence of NATO, remains essential in order to guarantee our security and that
of our Allies.

In 2010 the Government stated an intent to reduce our overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid-2020s. However, in recognition of the evolving security environment, including the developing range of technological and doctrinal threats, this is no longer possible, and the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads.

To ensure that our deterrent is not vulnerable to pre-emptive action by potential
adversaries, we will maintain our four submarines so that at least one will always be on a
Continuous At Sea Deterrent patrol. Our submarines on patrol are at several days’ notice
to fire and, since 1994, we do not target our missiles at any state. We remain committed
to maintaining the minimum destructive power needed to guarantee that the UK’s nuclear
deterrent remains credible and effective against the full range of state nuclear threats
from any direction.

We will continue to keep our nuclear posture under constant review in light of the international security environment and the actions of potential adversaries. We will maintain the capability required to impose costs on an adversary that would far outweigh the benefits they could hope to achieve should they threaten our, or our Allies’, security.”

UK nuclear weapons policy, according to the Integrated Review is as follows:  “The UK’s nuclear weapons are operationally independent and only the Prime Minister can
authorise their use. This ensures that political control is maintained at all times. We would
consider using our nuclear weapons only in extreme circumstances of self-defence,
including the defence of our NATO Allies.”