 On 28 June 2007 , the day after Gordon Brown had become Prime Minister , Miliband was sworn of the Privy Council and appointed Minister for the Cabinet Office and Chancellor of the Duchy of Lancaster , being promoted to the Cabinet . This meant that he and his brother , Foreign Secretary David Miliband , became the first brothers to serve in a British Cabinet since Edward and Oliver Stanley in 1938 . He was additionally given the task of drafting Labour 's manifesto for the 2010 general election . 
