LONDON, UNITED KINGDOM - NOVEMBER 10: Britain's Prime Minister David Cameron thinks during a question and answer session after he delivers a speech on EU reform and the UKs renegotiation at Chatham House on November 10, 2015 in London, England. Cameron on Tuesday formally launched his bid to renegotiate Britain's membership within the European Union, setting out four key demands for EU reform. (Photo by Kirsty Wigglesworth/Pool/Getty Images)
