Isabel Hilton hears how some African thinkers are now rejecting the idea of overseas aid. Western countries want to help poverty-stricken countries - but does their help exacerbate, not alleviate, problems? Dambisa Moyo, a Zambian banker based in London, wants to destroy the myth that it actually works. In her new book, she controversially argues that globalisation and the financial markets - often blamed for Africa's problems - are an opportunity for its success. Isabel challenges Dambisa to put her case to a group of guests.