ARLENE Foster and Martin McGuiness's office claimed on Tuesday night the two ministers only became aware of a civil service report warning of Brexit's grave implications for the north after a Freedom of Information request.
A joint statement from the Stormont leaders came after speculation that they may have breached the ministerial code by failing to publish a briefing paper highlighting negative consequences for the region when the UK leaves the EU.
The report by the European Policy and Co-ordination Unit in the Office of First Minister and Deputy First Minister (OFMDFM) was compiled last year but only released after the June 23 referendum following a Freedom of Information request, which is understood to have been submitted in February.
The analysis outlined up to two dozen ways in which officials believed Brexit would adversely affect the north's economy.
Sinn Féin's Martin McGuinness had indicated yesterday morning that the report's publication was vetoed by the then First Minister Peter Robinson.
The deputy first minister told the BBC that agreement was required between the DUP and Sinn Féin before the research could be published.
Mr McGuinness claimed the emergence of the paper's existence was a "non story", as his party had echoed its key findings during the referendum campaign.
The document's existence was revealed by the Detail website.
While the UK as whole backed leaving the EU, 56 per cent of people in Northern Ireland voted to remain.
Ulster Unionist leader Mike Nesbitt yesterday asked the Stormont speaker Robin Newton to see whether the decision to sit on the briefing paper breached the ministers' code on openness.
The Strangford MLA's query centres on an assembly question submitted days after the referendum asking the first and deputy first ministers to detail their Brexit contingency plan.
The ministers' response made no reference to the paper at the centre of the controversy.
"The first ministers were given an opportunity to respond to a written question on June 27 if there had been a scoping document and they had another opportunity at the Committee for the Executive Office (previously OFMDFM) to reveal that the EU unit had carried out work," Mr Nesbitt said.
"On both occasions they declined those opportunities – they did not inform the house of the existence of the document and now the question is did they mislead the chamber?"
SDLP MLA Sinead Bradley accused Stormont's big two of overseeing the "most secretive government in the history of devolution".
"Burying a civil service report on Brexit until after the referendum was a clandestine attempt to skew the public debate and should never have happened," the South Down representative said.
"That Martin McGuinness allowed the DUP to get away with holding it back reveals the extent of his impotence within this coalition."
The statement from the Executive Office said the document was commissioned by the head of the civil service and was among a range of working papers circulated at Stormont Castle.
It said the analysis was "not sent to ministers for consideration" and that Mrs Foster and Mr McGuinness only became aware of the paper after Freedom of Information requests.
"The Executive Office could not have taken sides in the referendum campaigns in the absence of an agreed position," the statement said.
"In any case the document contains well rehearsed arguments which were openly being aired during the referendum campaign and would have added nothing to the wider debate."
Meanwhile, Enda Kenny plans to host all-Ireland talks on the impact of Brexit within weeks.
The Taoiseach said the "all-island, all-Ireland conversation" in November will involve business people, members of civic society and political parties.
Details of the gathering will be revealed in the "near future", he told the Dáil, on its first day back after the summer break.
And he warned the process of Britain leaving the European Union could take a lot longer than some expect.
"I fear that this will run for quite some time," he said.
