Lord Carrington, Sting, Archbishop Desmond Tutu, John Peel, Joanna Trollope, David Attenborough and Baroness Betty Boothroyd have all, over the past year, made a three-minute appeal on behalf of a charity. So if you've ever listened to the Radio 4 Appeal and wondered how much charities raise or pondered who it is that donates, then Libby Purves will answer those questions and others.