CND are staging a protest at Downing Street to say 'No Nuclear War'. 
Here is a statement from CND:

We are alarmed by the threat of nuclear war in North East Asia and the wider Pacific region. North Korea continues to test nuclear weapons and missiles in defiance of the international community, while the US and its allies continue provocative actions, threats and exercises in or near North East Asia and the Pacific. There is a real danger that these actions will lead to the use of nuclear weapons by intention or miscalculation. There are no safe hands for nuclear weapons and any detonation of a nuclear device would be a humanitarian catastrophe with global impacts. Threatening and isolating the North Korean regime risks escalating the conflict rather than encouraging solutions.

We urge the UK Government to use all appropriate diplomatic, international and legal means to end nuclear threats, to push for negotiations with North Korea and a return to the Six-Party Talks involving China, North Korea, South Korea, Japan, Russia and the US. Both immediate and longer term solutions are needed including creating a zone free of nuclear weapons in North East Asia, a process to address the underlying causes of regional insecurity and conflict on the Korean Peninsula, and the promotion of peace, development and cooperative co-existence and security for all peoples in the region. 

We call on the UK Government to reject a military solution to the conflict and urgently use its influence to press for all involved to avoid and refrain from further provocative rhetoric or military exercises and tests.