 FORMER foreign secretary David Miliband revealed  last night he no longer has ambitions to become Prime Minister.  During a BBC Newsnight interview with Jeremy Paxman, Mr Miliband, beaten to the Labour leadership by his brother Ed, was asked:  Do you still dream of being prime minister?  He replied:  No, I don t .  Mr Miliband added:  The important thing is that I sleep soundly and the thing that wakes me up in the morning is my kids coming to jump on top of me.  He added: One of the causes that matters to  me is foreign policy, one of them is environmental policy and climate change, and one of them is the determined attempt of the Labour Party, under Ed s leadership, to win the next election.