LONDON (Reuters) - Most Britons who work more than a 48-hour week say they make mistakes because they are tired, according to a survey published on Wednesday. But while around one third of people believe working longer hours makes them more productive, another third found they had to redo work because their companies were inefficient, the Institute of Personnel and Development (IPD) survey found. Some 823 of the 7,987 people interviewed said they worked longer than 48 hours a week, 73 percent of whom admitted to making errors when tired. „The results suggest there is still scope for organisations and individuals to find ways of `working smarter rather than harder,“ said Melissa Compton-Edwards, author of the „Living to Work?“ survey. „Regularly burning the midnight oil could result in accidents or costly mistakes being made,“ she added.