Johnson, a former home secretary, will single out Theresa Villiers, the Northern Ireland secretary, who is pushing for Brexit, saying she ought to understand that the EU has been a steadfast source of political and financial support for the peace process.
During a trip to Northern Ireland on Thursday to campaign for the UK to remain in the EU, Johnson will say: “Northern Ireland’s ability to access the single market, coupled with the success of the Good Friday agreement, has brought about economic development for Northern Ireland as well as enhanced economic cooperation between north and south in Ireland.
“A withdrawal from the European Union could risk reversing that trend and undermining the economic and political progress made. By siding with the leave faction within the Conservative party, the Northern Ireland secretary Theresa Villiers is putting that progress at risk.”
Remain campaigners point to comments from the Irish ambassador, who told a parliamentary committee that the EU had helped improve relations between the UK and Ireland.
They claim Brexit would cost Northern Ireland about £100m of funding from the Peace programme, as well as money from the European regional development fund.
Villiers said it was “highly irresponsible to suggest that people in Northern Ireland will abandon their commitment to peaceful and democratic politics because of this referendum”.
She said: “There is steadfast support in Northern Ireland for the political settlement established by the Good Friday agreement and, as the Irish ambassador has made clear, a vote to leave will not affect the peace process.
“The peace process was delivered by the hard work of Northern Ireland’s leaders and successive UK and Irish governments, supported by the US. There is strong commitment in both the UK and Ireland to continue to work together for a peaceful and prosperous Northern Ireland, and leaving the EU will not change that.”
Villiers added: “With the money we would save from leaving, we could afford to fund the programmes the EU has supported in Northern Ireland and have money left over for other important priorities like the NHS.”
Remain campaigners in both Conservatives and Labour have repeatedly warned about the possibility of Scotland holding a second independence referendum if the UK votes to leave the EU, but there has been less scrutiny of the possible ramifications for Northern Ireland.
At a Downing Street press conference, Kenny suggested that the success of the Northern Ireland peace process was in part linked to the UK’s and the Irish Republic’s membership of the EU.
“The guns are silent. This has taken a great deal of work from so many people over so many years,” he said, when asked whether a UK exit would damage the peace process.
“It is important to say that the road out of inequality, the path out of that unfairness, is employment and opportunity. That is why we have shared trade missions to a number of locations, there is a great deal of cooperation with respect of issues of economics in Europe.
“We should not put anything like that at risk. From our perspective it would be a serious difficulty for Northern Ireland. I don’t want to see that happen. We work on the positive end of this – future benefits and potential coming from a strong Britain being part of a strong Europe and Ireland associated with that north and south.”
Some Sinn Féin politicians have recently called for a border poll on Irish reunification if there is a Brexit vote.
Martin McGuinness, the deputy first minister of Northern Ireland and former IRA chief of staff, said that if Britain voted to leave the EU there would be a “democratic imperative” to allow people on the island of Ireland to vote on reunification.
A border poll is unlikely to be granted by London even if the UK leaves the EU, and successive opinion polls in Northern Ireland have shown a substantial majority in the region favour remaining within the UK.
The largest unionist force in Northern Ireland, the Democratic Unionist party, is backing the campaign to leave the EU. However, the Ulster Unionist party’s ruling executive voted to support David Cameron’s campaign to remain in the EU.
This article was written by Rowena Mason Political correspondent, for theguardian.com on Thursday 7th April 2016 10.34 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010