Marcus Agius, the chairman of Barclays, resigned today, less than a week after the big British bank agreed to pay $450 million to settle accusations that it had tried to manipulate key interest rates to benefit its own bottom line, the New York Times DealBook blog reported today. The resignation comes as Barclays tries to limit fallout from the case, which is part of a broad investigation into how big banks set certain rates that affect borrowing costs for consumers and companies. Since striking a deal with American and British authorities last Wednesday, the Barclays management team has faced increasing pressure from politicians and shareholders to take action.