Prime Minister David Cameron has said there are "no limits" to what the Republic of Ireland and Britain can achieve together after the transformation in the relationship between the two countries in recent years.
Mr Cameron accompanied Taoiseach Enda Kenny on the short distance between No 10 Downing Street and Westminster for a reception last night, following a summit meeting at the end of a whirlwind day in London for Mr Kenny.
Mr Kenny said there had been a "very frank discussion" about Northern Ireland and hailed the "excellent co-operation" between the police on each side of the border.
"We want to see the Good Friday Agreement implemented in full and continue to work closely with the Executive to promote peace and stability and prosperity in Northern Ireland which is so important for everybody," he said.
Mr Cameron said he was determined not to allow recent "concerning developments" to "take us backwards".
"The world spotlight will be on Northern Ireland this year for the G8 and the celebrations of Derry/Londonderry City of Culture," he said. The PM said both countries had not begun to "tap" the potential of the relationship, which has prospered since the visit of the Queen to Ireland.
Following their talks at Number 10, Mr Cameron said the two governments would go "further and faster" in deepening relations.
"We are not letting our foot off the pedals; we want to go further and faster with this relationship," he said.