Roger John Liddle, Baron Liddle (born 14 June 1947) is a British political adviser and consultant who is principally known for being Special Adviser on European matters to prime minister Tony Blair and President of the European Commission, José Manuel Barroso. He also worked together with Peter Mandelson on books outlining the political philosophy of the Labour Party under Blair's leadership. He is chairperson of the international think tank Policy Network and Pro-Chancellor of the University of Lancaster.