HARDtalk is in Berlin as the city marks the 25th anniversary of the fall of the Berlin Wall - that extraordinary moment which dramatised the collapse of the communist system and the end of the Cold War. Stephen Sackur speaks to Mikhail Gorbachev, former president of the Soviet Union, architect of the policy of reform and openness which was supposed to revitalise the Soviet empire, but instead hastened its demise. How does he see east-west relations today?