He said: 'I don't get malaria'. The mother whose son gave away his anti-malaria tablets Jo Yirrell's story was a direct inspiration for my film. Not only her story, but also her amazing reaction to what happened to her, and her son Harry - the way she chose to use her experience and her grief to try to save the lives of other children. Parts of her are in the characters of both Mary and Martha," Curtis says. Mary, an American, is played by Hilary Swank; Martha, the Brit who loses her volunteer son, by a somewhat dowdy Brenda Blethyn. Jo is a considerably more charismatic woman, but she recognised parts of herself in the character. There was a bit when Martha's watching her son play rugby and she shouts: 'Get the ginger bastard! I wouldn't have said ginger, because Harry had red hair, but I would have said something equally raucous. After Harry's death, Jo's businessman husband David found it hard to discuss his son, whereas Jo was desperate to express her emotions. "If I hadn't got involved in malaria work, I would have gone completely mad," she says. "Now I can talk about Harry all the time and people have no choice but to listen," she laughs. At Harry's first dinner back home, Jo asked if he had obeyed her emails, reminding him to take the drugs. "He said: 'I don't get malaria,"" she recalls, at the table where the conversation took place at home in Leighton Buzzard, Bedfordshire. He hadn't used insect repellent or a mosquito net either. I said something about antimalarials being expensive but he said the children needed them more than he did - he had also sold his mobile and most of his clothes to buy things for them. I didn't think any more of it. There he was sitting there, as bright as anything. Eight days after his return, Harry complained of a headache. We put it down to the fact he'd been out with friends the night before when he hadn't had a drink for four months. He took painkillers and felt better, but two days later felt ill again. Jo made him a GP's appointment, but Harry didn't attend, because an attack of diarrhoea - another symptom of malaria - made him reluctant to leave home. The next day he rallied, but the following morning woke his parents saying he felt like death. They took him to nearby Stoke Mandeville hospital. After seven hours, blood tests confirmed he had falciparum malaria, the most dangerous strain of the disease, which kills red blood cells in the body, causing tissue to die through lack of oxygen. Harry was admitted to intensive care. "I thought: 'This is bad, but it's going to be all right, because this is England,"" says Jo. "One nurse mentioned malaria can be deadly, but my attitude was still: 'Yes, if you live in a mud hut in Africa, but here it's a hiccup."" But although malaria is usually treatable, speed is of the essence and the delays in having Harry diagnosed had lost him vital time. "When he arrived at the airport, he would have been riddled with malaria, but he was so fit he'd been able to fight it off for ages, before it finally took hold," Jo sighs. On intravenous quinine, Harry's condition initially stabilised, but after two days, he developed breathing difficulties. The malaria had caused pulmonary oedema, fluid on the lungs, making it hard for him to breathe. He was transferred to Centre for Tropical Medicine in Oxford. A consultant explained that Harry was seriously ill, but should eventually recover. "We talked about all the nursing he'd need, so even though Harry wasn't conscious we were still thinking: 'It's going to be all right."" This was Monday. At 3am on Wednesday morning, the hospital called saying Harry had taken a turn for the worse. We drove there like bats out of hell. Harry made it through the day and the Yirrells decided to stay the night in hospital. They made a brief trip home to see Harry's brothers. "The staff were acting very casually, but when we returned to hospital we were greeted by: 'We don't think he's going to survive the night."" The couple rushed to Harry's room. It was a horrendous scene, he had chest reins in to clear the fluid from his lungs, but his body wasn't getting enough oxygen and his organs were shutting down. David and I stood with him, holding his hand and stroking his hair. A nurse told me hearing was the last thing to go, so I just talked and I talked to him for the next 45 minutes telling him about all the people that loved him. And, very peacefully, he just died. The nurse asked if we'd like a lock of his hair and then we kissed him goodbye. My three teenage sons and parents expected us to be away all night, so a few hours later when we walked back through the door they instantly knew something had gone terribly wrong. Determined to salvage something from her grief, Jo was delighted to be recruited as an ambassador for the newly-formed charity Malaria No More UK. Two years after Harry's death, she visited the fishing village in Ghana where he spent the final, happy months of his life. I was petrified when I set off and there were tears but it was also very uplifting. I met so many people whom Harry loved and they loved him, which for a mother is just lovely. She also met several mothers who had lost several children to malaria: in Africa a child dies every minute from the disease. Their suffering is just as raw as mine, the difference is they've seen even more of their children die. It made me even more determined to work to see malaria eradicated in my lifetime. No one should have to lose a child like this, when it's so easily preventable. On Friday, the Yirrells watched Richard Curtis's version of her story. David didn't watch, he'd have found it very difficult, but the rest of us did - but privately, not all together. It was very hard for anyone who knew Harry. Funnily enough, even though I had a tear in my eye once or twice, I didn't get too upset and I sobbed all the way through [Curtis's] Love, Actually. Maybe it's because time's moved on, but I think it was just because it was all so beautifully done. "Losing a child rips out a part of you that you never fill in," Jo continues. You just learn to work round it and tape up the edges. It's funny, though - I'd give all the campaigning up, because it would mean I would have Harry back, but I absolutely love doing it. I know if he was alive he'd be doing it too. malarianomore.org.uk To watch Martha and Mary, visit: www.bbc.co.uk/iplayer