The UK's Brexit Secretary David Davis and EU chief negotiator Michael Barnier met again in Brussels on Monday, following last week's Brexit backstop drama. Davis threatened to resign over Prime Minister Theresa May's proposal for a temporary customs arrangement to avoid a hard border between Northern Ireland, which is part of the UK, and the Republic of Ireland, which is in the EU. Simon McGregor-Wood reports from the border on why it's such a crucial Brexit issue.
