What will the United Kingdom vote to leave the EU mean for Northern Ireland – and the rest of Ireland? BBC correspondent Edward Stourton revisits the city of Londonderry - or Derry - an area where people voted strongly to remain in the European Union, against the tide of the rest of the UK. There he discovers how locals fear that a border across the island of Ireland, between the Irish Republic which is still an EU member, and a post-Brexit Northern Ireland outside the EU, will disrupt their lives. Will the Northern Ireland peace process also be affected? And does the Brexit vote mean the survival of the United Kingdom itself is now in question?