CAMPAIGNERS have urged PM Boris Johnson to rethink his nuclear weapons policy after legal experts found that plans to increase Britain’s arsenal are in violation of international law.

An expert legal opinion commissioned by the Campaign for Nuclear Disarmament (CND) says that the proposed increase in nuclear warheads is a violation of the Non-Proliferation Treaty (NPT). 

Earlier this year Mr Johnson faced heavy criticism after a defence policy review proposed lifting the current cap on Trident’s nuclear warheads by over 40 per cent – from 180 to 260 – despite years of work towards disarmament.

Experts from the London School of Economics and Political Science, Professor Christine Chinkin and Dr Louise Arimatsu, have now set out why they believe the move could breach international law.

The pair said that the government’s plans would breach Article VI of the NPT, which commits signatories to pursuing ”negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament.” 

Professor Chinkin and Dr Arimatsu added that Britain would be in breach of international law were it to use or threaten to use nuclear weapons against a state party to the NPT.

Those who have long campaigned against weapons of mass destruction welcomed the legal opinion, saying that the experts’ view backs up international criticism of the government’s plans. 

CND general secretary Kate Hudson said: “The decision breaks with the gradual nuclear reductions implemented by successive governments going back nearly 30 years and is at odds with the decision by [US President Joe Biden and Russian President Vladimir Putin] to continue bilateral nuclear reductions.”

She said that the illegality of the increase would only strengthen support for the UN’s Treaty on the Prohibition of Nuclear Weapons, which entered into force this year.

“Boris Johnson’s decision to unilaterally start a new nuclear arms race is not what the world needs at this time of crisis,” Ms Hudson added.

Peace Pledge Union campaigns manager Symon Hill said: “This is the most militaristic British government for 30 years. Boris Johnson has announced the biggest percentage increase in British military spending since the Korean War. 

“When governments fuel war and ignore treaties, it is vital that we speak out against militarism and that people take nonviolent direct action to dismantle weapons and resist preparations for war.”

Politicians in the west of Scotland, where Britain’s warheads are held, have hit out at Ministry of Defence (MOD) plans to store more nukes north of the border, calling for the Clyde to be rid of the weapons.

Scottish Greens MSP Ross Greer said: “It is particularly galling that these weapons of mass extinction will be stockpiled in Scotland despite our repeated and clear rejection of them at the ballot box and through decades of protest. 

“I look forward to the day when an independent Scotland stands outside of Nato and as a proud signatory not only of the NPT but of the more recent Nuclear Weapon Ban Treaty.”

The International Campaign to Abolish Nuclear Weapons (ICAN) agreed with the legal opinion.

ICAN executive director Beatrice Fihn said: “The decision by the UK to violate the NPT and increase its arsenal of weapons of mass destruction threatens global security and stability.

“It not only violates the NPT, it also undermines trust in the NPT as an effective venue to achieve disarmament and non-proliferation. 

“In order to protect its people, the UK should immediately cease this build-up of nuclear arsenals and implement its obligations under the NPT and support the new Treaty on the Prohibition of Nuclear Weapons.”

An MOD spokeswoman told the Morning Star that the government remains “fully committed to the long-term goal of a world without nuclear weapons through gradual multilateral disarmament.

“Maintaining the UK’s nuclear deterrent capability at a minimum credible level is fully consistent with our international legal obligations, including those under Article VI of the Non-Proliferation Treaty,” she said.