The building currently houses Her Majesty’s Treasury. The Treasury is the government department responsible for public finances and economic policy. Back in the 11th century, during the reign of William the Conqueror, the first treasurer was probably a man called Henry 'The Treasurer', who is mentioned in the Domesday Book. The Treasury was literally where the King kept all his valuable possessions and the person in charge was the 'Lord Treasurer'. Over the centuries this position actually evolved into the role of 'Prime Minister'. Even today the more formal title for a Prime Minister is 'First Lord of the Treasury'. The person responsible for the department, the annual Budget, and other ministerial duties is the 'Second Lord of the Treasury', more often known as the 'Chancellor of the Exchequer'.