PARIS (Reuters) - Britain must find concrete proposals to tackle issues concerning the border between the United Kingdom and Ireland in the wake of Brexit, said French President Emmanuel Macron during a news conference with Irish Prime Minister Leo Varadkar.  It s up to the UK to come up with concrete proposals to minimize the impact of Brexit on the British/Irish border,  said Macron on Tuesday. Earlier this month, Varadkar had said Ireland wanted Britain to commit to a fallback option that would avoid a customs border returning to the island of Ireland, should its plan of keeping the closest possible ties with the EU fall through. 