At 10am on Sunday morning my brother Alaa drank his last sip of water in an Egyptian prison. He has been on hunger strike for more than 200 days and now, as world leaders arrive for Cop27, he has stopped drinking water. He’s been in prison for nine years. He’s not doing this now because he wants to die, but because it’s the only way he might get to live again. He’s been in prison for all but one year of his son’s life for his writings about democracy and technology, and his anti-authoritarian stance. The whole world is watching what happens in Sharm el-Sheikh, where I write this from, and he is staking his life on a belief that the world will today stand with him. The British prime minister, Rishi Sunak, is in Egypt right now. He wrote to me on Saturday saying he was committed to my brother’s release, both as a British citizen and as a defender of human rights. He will probably leave Egypt in a few hours. If Alaa isn’t on the plane with him, I fear for the worst. He’s already so weak from his hunger strike, I don’t know how many hours he can last without water. My mother is outside the prison now, waiting for the letter we usually receive on Mondays. It might be the last proof of life we ever get. I flew to Sharm el-Sheikh and arrived in the early hours of this morning to continue to campaign for my brother’s release. It’s a risk to return to Egypt, where I’ve also been imprisoned three times in my struggle to free my brother, but I have to do everything I can to save his life. He could die at any moment, and we wouldn’t even know. So we’re asking that the UK government from now on to at the very least secure “proof of life” once a day. So far, the UK government has not even been able to gain consular access to Alaa in prison, a basic request. It is an international humiliation for the UK government that the Egyptian regime can treat a British citizen in this way. Sunak has the opportunity to use his authority to fix this today. This is his first international visit, a test of his stature on the world stage. I can only hope and believe that in a few hours, Alaa will be on a plane back to London with him. Sanaa Seif is a film-maker, activist and sister of the imprisoned writer Alaa Abd el-Fattah