Three former Supreme Court judges have said the Government is breaching international law by continuing to arm Israel.

A letter to the Prime Minister – signed by more than 600 lawyers, academics and retired senior judges, including Baroness Brenda Hale, the former Supreme Court president, calls the current situation in Gaza “catastrophic”.

The letter sent on Wednesday says the International Court of Justice (ICJ) finding that there is a plausible risk of genocide being committed means Britain is legally bound to prevent it.

The 17-page document, seen by The Guardian, states: “While we welcome the increasingly robust calls by your government for a cessation of fighting and the unobstructed entry to Gaza of humanitarian assistance, simultaneously to continue (to take two striking examples) the sale of weapons and weapons systems to Israel and to maintain threats of suspending UK aid to [the UN relief organisation] Unrwa falls significantly short of your government’s obligations under international law.”

It comes as Rishi Sunak faces mounting pressure to act after the killing of seven aid workers, including three British citizens, in an Israeli strike on a convoy in Gaza.

The letter calls for the Government to push for a permanent ceasefire and to impose sanctions on those inciting genocide against Palestine.

On the continued supply for arms to Israel, it states: “The ICJ’s conclusion that there exists a plausible risk of genocide in Gaza has placed your government on notice that weapons might be used in its commission and that the suspension of their provision is thus a ‘means likely to deter’ and/or ‘a measure to prevent’ genocide.”

Senior retired judges normally refrain from weighing into politically sensitive issues, emphasising the significance of the letter. A prominent figure who put their name to the document includes Jonathan Sumption, the former Supreme Court justice.

Speaking to BBC Radio 4, he said: “The most important point is that Article 1 of the Genocide Convention requires states to do what they can to prevent genocide. Now, it hasn’t yet been determined whether what the Israelis are doing is genocide. The ICJ is considering that issue, but they have already ruled that there is a plausible case that that is what is going on in Gaza.”

He added: “It seems to me that we have a duty, as we do in international law, to prevent genocide and there is plausible case that is what is happening, you should do what you can to obstruct it.

“The deaths and the indiscriminate killings, these things are happening now.”

Lord Sumption said the British Government’s policy has always been to observe international law and it should therefore stop arming Israel.

The letter calls for the Government to take “immediate measures” to bring an end to “a risk of genocide” following developments in Gaza including the ICJ ruling, the rising death toll and the increased risk of famine due to the blocking of aid.

It also calls on the Prime Minister to do all he can to secure the release of hostages taken during the Oct 7 attacks.

Mr Sunak was sent another letter in October which raised concerns about the Government’s obligations to avert serious breaches of international humanitarian law and avoid complicity.