A fourth former supreme court justice has put his name to a letter warning Rishi Sunak that the UK is breaching international law by continuing to arm Israel, as the number of legal experts signing the letter rose to more than 750. Lord Carnwath joins Lady Hale, who was president of the UK’s highest court, and lords Sumption and Wilson, in urging ministers to act to prevent the “plausible risk” of genocide in Gaza. Another new signatory is Lord Brennan KC, the chair of the all-party parliamentary group on legal and constitutional affairs, who is the second former chair of the bar of England and Wales to add his name to the letter. The 17-page letter and legal opinion, also signed by four former court of appeal judges, more than 70 KCs, more than 100 partners and directors of law firms, and dozens of law professors, has added to already mounting pressure on the government to suspend arms sales in the wake of the Israeli airstrike that killed seven international aid workers, three of them British, on Monday. Citing both the international court of justice’s conclusion that a plausible risk of genocide exists in Gaza, and the UK’s obligations under the 1948 genocide convention, the letter states that halting weapons sales is a “‘means likely to deter’ and/or ‘a measure to prevent’ genocide”. It also calls for the government to work towards a permanent ceasefire, impose sanctions against those inciting genocide against Palestinians, restore funding to the UN agency for Palestinian refugees, Unrwa. UK support for Unrwa was withdrawn after Israel’s so-far unsubstantiated allegations that 12 staff were involved in the Hamas attacks in southern Israel on 7 October. The letter says the decision must be reversed for “effective entry and distribution of the means of existence to Palestinians in Gaza, and by extension the prevention of genocide”. The fifth action it says the government should take in light of international law is “to suspend the 2030 road map for UK-Israel bilateral relations and negotiations towards an enhanced trade agreement, and to initiate a review into the suspension of the UK’s bilateral trade agreement with Israel and consider the imposition of sanctions”. The number of signatories and the fact the letter has been signed by senior retired judges, who rarely comment publicly on politically sensitive issues, makes the message difficult to ignore. The letter has also increased pressure on the government to publish the legal advice it has received on whether UK arms are at risk of being involved in a breach of humanitarian law. Ministers continue to say that they keep the advice under review and act accordingly.