The UK Attorney General’s Office (AGO) is investigating whether the Prime Minister, Theresa May, and the Defence Secretary, Michael Fallon, can be taken to court for conspiring to commit war crimes with Trident nuclear weapons.

Nearly 400 people from five campaign groups are bidding to prosecute the Westminster government for breaching criminal law by being prepared to unleash a devastating nuclear strike on Moscow or other foreign cities from submarines based on the Clyde.

Recent statements by May and Fallon that they would be willing to launch Trident missiles show that they are planning “indiscriminate mass slaughter”, campaigners say. They have begun prosecutions in local courts, but been told that the Attorney General’s permission is needed to proceed.

With the help of leading nuclear and human rights lawyers, they have submitted a large dossier of evidence to the AGO in London. “Work on the application is ongoing,” an AGO spokeswoman told the Sunday Herald.

“There is a considerable amount of material to work through and we will provide a response as soon as reasonably practicable.”

She added: “The Attorney will consider whether there is sufficient evidence to prove the charges proposed and, if so, whether a prosecution is required in the public interest. The Attorney will act independently of government when taking this decision.”

Local groups in England and Wales have come together under the banner of the Public Interest Case Against Trident (PICAT), backed by the Institute for Law, Accountability and Peace. They are being assisted by the well-known human rights lawyer, Kirsty Brimelow QC, and by the nuclear legal expert, Professor Nick Grief, both from Doughty Street Chambers in London.

Their draft indictment accuses May and Fallon of breaching section 51(1) of the International Criminal Court Act 2001 and section 1 of the Criminal Law Act 1977. It says they “conspired together and with other persons to commit the war crime of excessive incidental death, injury, or damage by continuing and/or agreeing a policy to maintain the capability to launch a nuclear attack on targets in and around Moscow.”

The two ministers did this, the indictment continues, knowing that such an attack would kill or injure civilians or cause “widespread, long-term and severe damage to the natural environment”. The destruction caused would be “clearly excessive in relation to the concrete and direct overall military advantage anticipated.”

The United Nations International Court of Justice in The Hague ruled in 1996 that the use or threat of nuclear weapons was illegal. The decision was made on the casting vote of the court’s president at the time, Judge Mohammed Bedjaoui from Algeria.

Since then he has revealed his personal opinion that the UK’s deployment of over 100 warheads with an approximate yield of 100 kilotons each is illegal. “The use of even a single such warhead in any circumstance…would inevitably violate the prohibitions on the infliction of unnecessary suffering and indiscriminate harm,” he said.

Angie Zelter, a veteran peace campaigner and PICAT organiser, argued that the ideology of nuclear deterrence undermines international legal order. “We are trying to present our public interest case to enable a court of law to examine our evidence and prevent the disaster of a nuclear holocaust before it is too late,” she said.

Another PICAT organiser, Robbie Manson, said: “The making of detailed technical plans to bring about the indiscriminate mass slaughter of multiple millions of innocent non-combatant civilian Muscovite citizens is a clear and manifest breach of the fundamental codes of international humanitarian criminal law.”

The Ministry of Defence said it would be “inappropriate” to comment. “The application for prosecution is a matter for the Attorney General,” said an MoD spokesperson.