Three hundred prominent economists have signed a joint letter calling for new rules that would oblige companies to report publicly taxable activities on a country-by-country basis. In the letter, addressed to world leaders, economists say poor countries are the biggest losers from tax havens. Among the signatories is best-selling author Thomas Piketty and 2015 Nobel Prize-winning economist Angus Deaton. The letter is published ahead of the UK government's anti-corruption summit, which will be attended by politicians from about 40 countries as well as World Bank and IMF representatives.